An easy-to-make recipe for high altitude peanut butter sheet cake. This cake is moist and dense, with the texture of a cakey cookie bar, frosted with fudge-like peanut butter icing.
You might also love these high altitude recipes for chocolate peanut cluster cupcakes, flourless peanut butter chocolate chip cookies, and salted peanut butter blondies.
This site contains affiliate links. As an Amazon associate, I earn from qualifying purchases. This means that I may make a small commission if you purchase a product using those links. This in no way affects my opinion of those products and services. All opinions expressed on this site are my own.
Why You’ll Love This Recipe
Easy to Make. You don’t even need a mixer to make the cake or the icing, just a bowl, whisk and spatula.
Moist for Days. This cake is super moist, even days after baking.
Customizable. Use creamy or crunchy peanut butter, depending on if you like the texture of chopped peanuts or not. And instead of the peanut butter icing, you could frost the cake with chocolate ganache, or even add chocolate chips to the cake batter.
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. Adds moisture and flavor.
- Peanut Butter. I used creamy peanut butter, but you can use crunchy, too. Any type of peanut butter will work.
- Whole Milk. Moisture.
- Sugar. A combination of granulated sugar and light brown sugar adds sweetness and moisture.
- Eggs. Gives the cake structure and moisture.
- Vanilla Extract. Flavor.
- All-Purpose Flour. Gives the cake structure and strength.
- Baking Powder. Leavening agent, so the cake rises as it bakes.
- Salt. Balances the sweetness.
Frosting
- Butter. Use either salted or unsalted. If you use salted, you might want to omit the extra salt from the recipe.
- Peanut Butter. Again, either crunchy or creamy peanut butter will work, just depending on what you want for the texture.
- Powdered Sugar. Sweetens and thickens the icing.
- Vanilla Extract. Flavor.
- Salt. Balances the sweetness.
Instructions
Cake
- Preheat the oven to 350 F, and position a rack in the center of the oven. Lightly spray an 8 or 9 inch square baking pan with non-stick baking spray, or line with parchment paper.
- In a saucepan over medium heat, melt the butter. Add the peanut butter and milk, and stir until smooth. Remove from the heat.
- In a bowl, whisk together the warm peanut butter mixture with the granulated sugar and light brown sugar. Whisk in the eggs and vanilla.
- Separately, combine the flour with the baking powder and salt. Add the dry ingredients to the wet ingredients and stir together just until combined. The batter will be thick.
- Spread the batter into the prepared pan, and bake for about 30-35 minutes (for an 8 inch pan) or 25-30 minutes (for a 9 inch pan), until a toothpick or cake tester inserted in the center comes out clean, or with moist crumbs clinging to it.
- Let the cake cool in the pan for 1 hour, then add the icing while the cake is warm.
Icing
- In a saucepan over medium heat, melt the butter. Stir in the peanut butter until smooth. Stir in the powdered sugar, vanilla and salt. Stirring constantly with a rubber spatula, bring the frosting to a simmer, and remove from the heat when it begins to bubble.
- Immediately, pour the frosting over the cake. Let sit for several hours, until the frosting is firm and set. Sprinkle the top with flaky finishing salt, then cut into squares.
Recipe Variations
- Chocolate Ganache. For a less sweet dessert, this peanut butter sheet cake is fantastic with chocolate ganache, instead of the peanut butter icing. Find my ganache recipe in this post.
- Chocolate Chips. For a delicious chocolate chip peanut butter cake, just add about 1/2 – 3/4 cup semi sweet chocolate chips to the cake batter.
Be sure to read all of my BAKING FAQs where I discuss ingredients, substitutions and common baking questions, so that you can be successful in your own baking!
Frequently Asked Questions
Will this recipe work with all natural peanut butter?
While I haven’t tested it with all natural peanut butter, I think it would work just fine in the cake batter. In the icing, though, the separation of the oil may cause issues.
How should I store the leftover peanut butter sheet cake?
Keep the cake in an airtight container at room temperature for up to 3 days.
You Might Also Like
Please check out my Amazon Shop for a curated collection of some of my favorite cake pans from trusted brands, baking tools, ingredients, pretty things and fashion finds. I recommend products that I buy and use every day!
Did you love today’s recipe? Please rate the recipe and let me know in the comments what you thought! Also, be sure to follow Curly Girl Kitchen on Instagram, and tag me when you try one of my recipes so I can see all your delicious creations!
High Altitude Peanut Butter Sheet Cake
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 or 9 inch baking pan
Ingredients
Cake
- ½ cup unsalted butter
- â…“ cup creamy peanut butter
- ¼ cup whole milk
- â…” cup granulated sugar
- â…” cup light brown sugar, lightly packed
- 2 large eggs
- 2 tsp vanilla extract
- 2 cups + 2 tbsp all-purpose flour, fluffed, spooned and leveled
- 1 ½ tsp baking powder
- ½ tsp coarse Kosher salt (if using table salt, use half the amount)
Frosting
- ½ cup unsalted butter
- ¼ cup creamy peanut butter
- 1 cup powdered sugar
- ½ tsp vanilla extract
- â…› tsp coarse Kosher salt
- flaky finishing salt (if using table salt, use half the amount)
Instructions
Cake
- Preheat the oven to 350 F, and position a rack in the center of the oven. Lightly spray an 8 or 9 inch square baking pan with non-stick baking spray, or line with parchment paper.
- In a saucepan over medium heat, melt the butter. Add the peanut butter and milk, and stir until smooth. Remove from the heat.
- In a bowl, whisk together the warm peanut butter mixture with the granulated sugar and light brown sugar. Whisk in the eggs and vanilla.
- Separately, combine the flour with the baking powder and salt. Add the dry ingredients to the wet ingredients and stir together just until combined. The batter will be thick.
- Spread the batter into the prepared pan, and bake for about 30-35 minutes (for an 8 inch pan) or 25-30 minutes (for a 9 inch pan), until a toothpick or cake tester inserted in the center comes out clean, or with moist crumbs clinging to it.
- Let the cake cool in the pan for 1 hour, then add the icing while the cake is warm.
Icing
- In a saucepan over medium heat, melt the butter. Stir in the peanut butter until smooth. Stir in the powdered sugar, vanilla and salt. Stirring constantly with a rubber spatula, bring the frosting to a simmer, and remove from the heat when it begins to bubble.
- Immediately, pour the frosting over the cake. Let sit for several hours, until the frosting is firm and set. Sprinkle the top with flaky finishing salt, then cut into squares.
Linda S.
I am so curious about this cake and have never made a cake where I melt the butter, milk and peanut butter. I’m used to the creaming method or the dry/wet/dry/wet/dry incorporation. Is the melted butter with peanut butter and milk similar to that method? I’m hoping to make this recipe but using gluten-free flour. I love what you do! I live at 7300 ft so I make little adjustments to your recipes. Thanks for your blog and weekly letter. It keeps me inspired.