A high altitude recipe for a classic Boston cream pie, with layers of buttery yellow cake, homemade vanilla bean custard, and rich chocolate ganache.
You might also love this chocolate fudge cake with ganache, white velvet cake, and red velvet cake with cream cheese buttercream.
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What is a Boston Cream Pie?
If you’re not familiar with a Boston cream pie, it’s actually not a pie at all, but a cake with a cream or custard filling, and it’s the official dessert of Massachusetts. This dessert dates back to the 1800s, when cakes were often baked in pie pans, so the terms “cake” and “pie” were often used interchangeably.
Why You’ll Love This Recipe
Elegant and Classic. I love a good classic cake recipe, and this cake has so many good things going on. The soft, buttery cake, creamy custard and rich chocolate ganache makes a delicious dessert that’s hard to stop eating.
Fantastic Leftover. My favorite way to eat this cake when it’s leftover, is to pour milk over a slice of cake (sort of like a tres-leches cake, which is soaked in lots of milk). Then I’ll warm it in the microwave for about 45 seconds at 50% power. This will soften and moisten the cake and custard, and slightly melt the ganache, and it’s just so incredibly delicious like this.
High Altitude Tested. I develop all the recipes on my site for Denver’s altitude of 5,280 feet. If you’re at a lower or higher elevation, please see my FAQs for guidance on adjusting recipes for your altitude.
See the recipe card at the end of the post for the full ingredients list and instructions.
Ingredients
Cake
- Butter + Oil. A combination of melted butter and vegetable oil adds fat, flavor and moisture.
- Sugar. Granulated sugar adds sweetness and moisture.
- Eggs. Gives the cake strength and adds richness.
- Vanilla Extract. Flavor.
- Buttermilk + Sour Cream. A combination of buttermilk and sour cream adds moisture, fat and acidity, for a soft, tender cake crumb.
- Cake Flour. Gives the cake structure and strength. If you don’t have cake flour, you can also use all-purpose flour.
- Baking Powder. Leavens the cake, making it rise as it bakes.
- Salt. Balances the sweetness.
Custard
- Sugar. Sweetens the custard.
- Corn Starch. Thickens the custard so that it can support the weight of the top cake layer.
- Milk. Use whole milk for a more flavorful custard.
- Egg Yolks. Add richness and flavor.
- Vanilla. Use a good quality vanilla extract, or the seeds scraped from a vanilla bean for the best flavor and pretty specks of vanilla. You can also use vanilla bean paste.
- Butter. After cooking the custard, a little butter adds richness and flavor.
Ganache
- Chocolate. Good quality dark chocolate (between 55-60% cacao) will make the best chocolate ganache.
- Cream. Be sure to choose heavy whipping cream, not half and half or table cream.
Instructions
Cake
- Preheat the oven to 350 F, position a rack in the center of the oven, and spray the bottoms of two 8-inch round cake pans with non-stick baking spray.
- In a bowl, sift together the flour, sugar, baking powder, and salt.
- Add the milk, sour cream, eggs, melted butter, oil, and vanilla, and whisk until smooth.
- Divide the batter between the pans. Bake on the center oven rack for about 20-25 minutes, until a cake tester comes out clean.
- Set the pans on a cooling rack, cover loosely with a clean kitchen towel, and cool completely before assembling your cake.
Custard
- In a saucepan, whisk together the sugar and corn starch. Slowly whisk in the milk, then the egg yolks, until smooth.
- Cook the custard over medium heat, whisking constantly. As the custard starts to thicken, it may seem lumpy or curdled at first, but just keep whisking and it will smooth out. When the custard has thickened, continue to cook and whisk for 1 minute, to fully activate the corn starch. This whole process should take about 8-10 minutes.
- Remove from the heat and vigorously whisk in the vanilla and butter until smooth. Cover and refrigerate the custard until your cakes are cool, and you’re ready to assemble your cake. Use a spoon to stir the custard to loosen it up and smooth out the texture, before filling your cake.TIP: If the custard seems too thick for your liking, you can whisk in some cold milk or cream, 1 tablespoon at a time, whisking vigorously until smooth. Be careful with thinning it out, though: if the custard is too soft, it won’t be able to support the weight of the top cake layer, without squishing out.
- Remove the cakes from the pans, and set one cake on a cake plate or pedestal. To keep the cakes moist, since this is a naked cake, I like to brush the baked cakes with several tablespoons of milk.
- Spread the custard in an even layer over the cake, stopping at the edges, or fill a piping bag with the custard and pipe it onto the cake.
- Set the second cake on top of the custard, and gently press it down a little, but not so much that you squish the custard out the sides.
Ganache
- Finely chop the chocolate, scrape 3 ounces into a bowl, and set aside. You can also use chocolate chips, instead of chopped chocolate. (Reserve 1/2 ounce of the chopped chocolate for decorating.)
- Warm the cream in the microwave or in a saucepan on the stove, just until it begins to simmer around the edges.
- Pour the hot cream over the chocolate and stir until smooth and shiny.
- If your ganache is thin and runny, let it cool at room temperature for 10-20 minutes, stirring occasionally, until it’s thick enough that it won’t run off the top of the cake. Pour the ganache over the cake, gently spreading it towards the edges so it just starts to drip over the edges, but doesn’t run down the sides of the cake.
- Let the ganache cool and set for a few minutes, then sprinkle with the remaining 1/2 ounce of chopped chocolate.
- You can serve the cake immediately, or let the ganache set for about 30 minutes first.
6-Inch Cake
When I created and published this recipe several years ago, I baked this cake in two 6-inch pans (with a 3-inch depth), for a taller cake. The preparation and bake time is the same for this size. I’ve come to prefer the thinner layers of the 8-inch cake, though, as it provides more surface area for the custard and ganache.
Be sure to read all of my BAKING FAQs where I discuss ingredients, substitutions and common questions with cake making, so that you can be successful in your own baking! I also suggest reading these comprehensive posts on making Perfect American Buttercream, How to Stack, Fill, Crumb Coat and Frost Layer Cakes and How to Use Piping Bags.
Frequently Asked Questions
Yes, custard and pastry cream are pretty much the same thing. I have a post just on making vanilla custard. You’ll note that I made the custard much thicker for this Boston cream pie, so that it can support the weight of the top cake layer.
Yes, if you double the recipe, you should bake the cake in two 9-inch cake pans.
Since the custard is perishable, you should refrigerate the assembled cake in an airtight container to keep the naked cake layers from drying out. Let the leftover cake warm up to room temperature before serving.
Naked cakes tend to dry out more quickly, simply because they lack the layer of buttercream around the edges which keeps in moisture. This is also a butter-based cake, which tends to be more dry than cakes with lots of oil. I like to brush the baked and cooled cakes with two tbsp of milk (on each cake) to add extra moisture, as I assemble the layers. My favorite way to eat this cake when it’s leftover, is to pour 2 tablespoons of milk over a slice of cake (sort of like a tres-leches cake, which is soaked in lots of milk). Then I’ll warm it in the microwave for about 45 seconds at 50% power. This will soften and moisten the cake and custard, and slightly melt the ganache, and it’s just so incredibly delicious like this.
You Might Also Like
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High Altitude Boston Cream Pie
All recipes on Curly Girl Kitchen are developed for high altitude at 5,280 feet. See FAQs for adjusting to higher or lower elevations.
Equipment
- 8-inch round cake pans (x2)
Ingredients
Cake
- 1 ½ cups cake flour, fluffed, spooned and leveled
- 1 cup granulated sugar
- 1 ¼ tsp baking powder
- ½ tsp coarse Kosher salt (if using table salt, use half the amount)
- ⅔ cup whole milk
- ⅓ cup full-fat sour cream
- 2 large eggs
- 6 tbsp unsalted butter, melted
- 2 tbsp vegetable oil
- 1 tsp vanilla extract
Custard
- ⅓ cup granulated sugar
- 3 tbsp corn starch
- 1 cup whole milk
- 3 large egg yolks
- 1 tsp vanilla bean paste (or the seeds scraped from 1 vanilla bean)
- 2 tbsp unsalted butter
Ganache
- 3 ½ oz semi sweet or dark chocolate, finely chopped
- 3 oz heavy whipping cream
Instructions
Cake
- Preheat the oven to 350 F, position a rack in the center of the oven, and spray the bottoms of two 8-inch round cake pans with non-stick baking spray.
- In a bowl, sift together the flour, sugar, baking powder, and salt.
- Add the milk, sour cream, eggs, melted butter, oil, and vanilla, and whisk until smooth.
- Divide the batter between the pans. Bake on the center oven rack for about 20-25 minutes, until a cake tester comes out clean.
- Set the pans on a cooling rack, cover loosely with a clean kitchen towel, and cool completely before assembling your cake.
Custard
- In a saucepan, whisk together the sugar and corn starch. Slowly whisk in the milk, then the egg yolks, until smooth.
- Cook the custard over medium heat, whisking constantly. As the custard starts to thicken, it may seem lumpy or curdled at first, but just keep whisking and it will smooth out. When the custard has thickened, continue to cook and whisk for 1 minute, to fully activate the corn starch. This whole process should take about 8-10 minutes.
- Remove from the heat and vigorously whisk in the vanilla and butter until smooth. Cover and refrigerate the custard until your cakes are cool, and you're ready to assemble your cake. Use a spoon to stir the custard to loosen it up and smooth out the texture, before filling your cake.TIP: If the custard seems too thick for your liking, you can whisk in some cold milk or cream, 1 tablespoon at a time, whisking vigorously until smooth. Be careful with thinning it out, though: if the custard is too soft, it won't be able to support the weight of the top cake layer, without squishing out.
- Remove the cakes from the pans, and set one cake on a cake plate or pedestal. To keep the cakes moist, since this is a naked cake, I like to brush the baked cakes with several tablespoons of milk.
- Spread the custard in an even layer over the cake, stopping at the edges, or fill a piping bag with the custard and pipe it onto the cake.
- Set the second cake on top of the custard, and gently press it down a little, but not so much that you squish the custard out the sides.
Ganache
- Finely chop the chocolate, scrape 3 ounces into a bowl, and set aside. You can also use chocolate chips, instead of chopped chocolate. (Reserve 1/2 ounce of the chopped chocolate for decorating.)
- Warm the cream in the microwave or in a saucepan on the stove, just until it begins to simmer around the edges.
- Pour the hot cream over the chocolate and stir until smooth and shiny.
- If your ganache is thin and runny, let it cool at room temperature for 10-20 minutes, stirring occasionally, until it's thick enough that it won't run off the top of the cake. Pour the ganache over the cake, gently spreading it towards the edges so it just starts to drip over the edges, but doesn't run down the sides of the cake.
- Let the ganache cool and set for a few minutes, then sprinkle with the remaining 1/2 ounce of chopped chocolate.
- You can serve the cake immediately, or let the ganache set for about 30 minutes first.
Video
Notes
- Store leftover cake in an airtight container in the refrigerator for up to 2 days. Let the leftover cake warm up to room temperature before serving.
- Naked cakes tend to dry out more quickly, simply because they lack the layer of buttercream around the edges which keeps in moisture. I like to brush the baked and cooled cakes with two tbsp of milk (on each cake) to add extra moisture, as I assemble the layers.
- My favorite way to eat this cake when it’s leftover, is to pour 2 tablespoons of milk over a slice of cake (sort of like a tres-leches cake, which is soaked in lots of milk). Then I’ll warm it in the microwave for about 45 seconds at 50% power. This will soften and moisten the cake and custard, and slightly melt the ganache, and it’s just so incredibly delicious like this.
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Definitely was not as pretty as yours. For a first time make, it wasn’t to bad.
Fabulous!
Exquisite! I will always consult Curlygirl before any other recipe. The best cake, custard and ganache I’ve ever tried. Using real vanilla bean is well worth the cost.
Such a nice comment, thank you! 🙂
Made it for a birthday and it was delicious! Everyone loved it and it actually looked pretty good.
Stunning and delicious! Fantastic recipe!!
The cake was ok, not my favorite. The custard filling was so thick that it tasted funny. I did thin it out but it still had a cornstarch flavor to me. I wasnt interested in piping the filling, so a different recipe would be better for me next time.