An easy high altitude recipe for a super moist and chocolatey Denver sheet cake. This classic chocolate sheet cake is frosted with sweet, fudgy icing and sprinkled with chopped walnuts.
You might also love these high altitude recipes for chocolate crumb cake, yellow birthday sheet cake with chocolate frosting, and chocolate cupcakes.
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So What is a Denver Sheet Cake?
A Denver sheet cake is a classic dessert in the mid-west. It’s a very thin cake, no more than an inch high, that’s usually baked in a rimmed sheet pan or baking sheet. It’s a super moist and tender cake, thanks to the addition of buttermilk in the cake batter. The chocolate flavor is often fairly mild rather than super dark, with a sweet, milky chocolate glaze or icing that’s typically sprinkled with chopped walnuts.
It’s a recipe that first appeared in the Denver Jr. League Cookbook, and it now goes by many variations and names, such as Texas sheet cake, chocolate brownie cake, buttermilk brownies, brownie sheet cake, chocolate brownie cake, chocolate sheet brownies, Mexican chocolate cake and Texas brownie cake, to name a few.
Why You’ll Love This Recipe
Easy to Make. You won’t need a mixer or any special equipment to make this chocolate sheet cake, and it comes together quickly.
Feeds a Crowd. You’ll get 24 squares of cake from this recipe, so it’s ideal for parties, picnics and potlucks. I’ve lived in Colorado since I was 12, and this is the type of dessert that my friends’ moms would often make for our late night movie marathons and sleepovers on Friday nights. A piece of this cake is fantastic eaten slightly warm, with a scoop of vanilla ice cream melting on top.
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
- Buttermilk. You can use low fat or full fat buttermilk, which adds moisture and acidity for a very tender cake.
- Butter + Vegetable Oil. Unsalted butter adds moisture and flavor to the cake, while the oil keeps is soft and moist.
- Eggs. Gives the cake structure and strength.
- Vanilla Extract. Flavor.
- Hot Water. Again, this adds moisture, but the hot water also helps to “bloom” the cocoa powder for a richer flavor.
- Flour. All purpose flour gives the cake structure.
- Granulated Sugar. Adds sweetness and moisture.
- Cocoa Powder. I always use unsweetened Dutch processed cocoa powder for my baking, and have not tested this recipe with natural cocoa powder.
- Baking Soda. Leavening agent, so the cake puffs up as it bakes and isn’t dense.
- Salt. Balances the sweetness and enhances flavors.
Icing
- Butter + Milk. You’ll be starting by melting together unsalted butter and whole milk, which will thin the icing and give it a rich flavor.
- Cocoa Powder. Again, use Dutch processed cocoa powder for the best flavor.
- Vanilla Extract. Flavor.
- Powdered Sugar. Thickens and sweetens the icing.
- Walnuts. Optional, but these add a lovely nutty crunch and texture to contrast the soft cake.
Instructions
Cake
- Preheat the oven to 350 F, and position a rack in the center of the oven. Lightly spray a 13×18 inch rimmed baking sheet with non-stick baking spray, or line with parchment paper.
- In a large bowl, whisk together the buttermilk, melted butter, oil, eggs and vanilla. Very slowly, add the hot water to gradually temper the eggs so as not to scramble them, whisking until well combined.
- In a separate bowl, sift together the flour, sugar, cocoa powder, baking soda and salt. Add the dry ingredients to the wet, whisking for 10-15 seconds until combined. The batter will be thin.
- Pour the batter into the prepared pan. Bake the cake for about 25 minutes, until the top springs back when gently touched.
- Set the pan on a cooling rack, and make the icing.
Icing
- In a saucepan, heat the butter and milk over medium heat, until the butter is melted. Whisk in the cocoa powder and vanilla, then remove from the heat.
- Gradually add the powdered sugar, whisking the icing vigorously until smooth. If there are still lumps of powdered sugar that you can’t whisk out, you can beat the icing for about 30 seconds with an electric mixer.
- Immediately, spread the icing over the hot cake, then sprinkle with the chopped walnuts. The icing will crust over quickly.
- Let the cake cool completely for several hours before cutting into 24 squares.
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
Store leftover cake in an airtight container at room temperature for up to 3 days.
You can use any type of cocoa powder in the icing, but I’ve only tested this cake with Dutch processed cocoa powder.
Yes, you can make a smaller and thicker sheet cake by baking the same amount of batter in a 9×13 inch baking pan. See my chocolate sheet cake recipe to estimate the bake time.
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High Altitude Denver Chocolate 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
- 13×18 Rimmed Baking Sheet
Ingredients
Cake
- 1 cup buttermilk room temperature
- ½ cup unsalted butter, melted
- ½ cup vegetable oil
- 2 large eggs, room temperature
- 1 tbsp vanilla extract
- 1 ½ cups very hot water
- 2 ¼ cups all-purpose flour, fluffed, spooned and leveled
- 1 ¾ cups granulated sugar
- ½ cup unsweetened Dutch processed cocoa powder
- 1 tsp baking soda
- ½ tsp coarse Kosher salt (if using table salt, use half the amount)
Icing
- ½ cup unsalted butter, melted
- ¼ cup whole milk
- ¼ cup unsweetened Dutch processed cocoa powder
- 1 tsp vanilla extract
- 2 – 2 ½ cups powdered sugar
- ½ cup walnuts, chopped
Instructions
Cake
- Preheat the oven to 350 F, and position a rack in the center of the oven. Lightly spray a 13×18 inch rimmed baking sheet with non-stick baking spray, or line with parchment paper.
- In a large bowl, whisk together the buttermilk, melted butter, oil, eggs and vanilla. Very slowly, add the hot water to gradually temper the eggs so as not to scramble them, whisking until well combined.
- In a separate bowl, sift together the flour, sugar, cocoa powder, baking soda and salt. Add the dry ingredients to the wet, whisking for 10-15 seconds until combined. The batter will be thin.
- Pour the batter into the prepared pan. Bake the cake for about 25 minutes, until the top springs back when gently touched.
- Set the pan on a cooling rack, and make the icing.
Icing
- In a saucepan, heat the butter and milk over medium heat, until the butter is melted. Whisk in the cocoa powder and vanilla, then remove from the heat.
- Gradually add the powdered sugar, whisking the icing vigorously until smooth. If there are still lumps of powdered sugar that you can't whisk out, you can beat the icing for about 30 seconds with an electric mixer.
- Immediately, spread the icing over the hot cake, then sprinkle with the chopped walnuts. The icing will crust over quickly.
- Let the cake cool completely for several hours before cutting into 24 squares.
This cake is soft and moist with a fine crumb and big chocolate flavor. I’m a seasoned baker, but moved to the mountains (6200 feet) six years ago and have been on a learning curve ever since. Your website is a godsend. Just made this chocolate cake for a casual dinner with neighbors last night and it was a major hit!
When I was about 14 years old I learned a recipe from a woman from Texas that included boiling water. It was the only one I had heard of until many years later and it was delicious Like so many childhood recipes that get forgotten, I tried it again, at high altitude, with dismalI results. Thank you for this recipe which brought back such wonderful memories!
One question… can I halve the recipe and bake in a quarter sheet pan?
I’m so glad everyone loved it! Yes, you can definitely cut this in half for a quarter sheet pan.
Can I use cake flour in this recipe ? Hoping to make today for son’s birthday!
I haven’t tested this recipe with cake flour, but I imagine it would work, although you may need to add 1-2 tablespoons more flour.
I did use cake flour, adding a little more as you suggested. It came out great! Thank you for this delicious recipe!