High Altitude Chocolate Sheet Cake

The easiest and best high altitude recipe for chocolate sheet cake that’s tender, moist and flavorful with sour cream and rich Dutch-processed cocoa powder, and frosted with creamy dark chocolate ganache. Decorate your cake with chocolate chips, chopped chocolate, or colorful sprinkles for a fun and delicious birthday cake that everyone will love!

You might also love these high altitude recipes for mini chocolate cake for two, chocolate caramel toffee layer cake, and one layer chocolate chestnut cake.

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Why You’ll Love This Recipe

No Mixer Needed. You don’t need a mixer for the chocolate cake batter or the ganache frosting. Just quickly mix everything up with a bowl and whisk.

Enjoy Warm or Cold. One of the best things about this chocolate sheet cake is that it requires very little planning ahead. Unlike a layer cake which needs to be baked and cooled well in advance so that you can assemble and frost it, you can enjoy this cake while it’s still a little warm from the oven. You can spread the ganache on while it’s warm, too, and the combination of soft cake with gooey ganache is a chocolate lover’s dream.

Soft and Moist for Days. Today’s high altitude chocolate sheet cake is based on my popular chocolate layer cake. This is a favorite recipe with high altitude bakers for its exceptional flavor, texture and moisture. Chocolate cake with sour cream really is the best kind of chocolate cake.

Versatile Presentation. Sprinkle your cake with mini chocolate chips or chopped chocolate, or with a handful of colorful sprinkles for a more festive, birthday party cake.

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

• Flour. All-purpose flour gives the cake structure and strength.
• Sugar. Granulated sugar adds sweetness and moisture.
• Cocoa Powder. Be sure to use a good-quality Dutch processed cocoa powder for the best flavor. Natural cocoa powder will not give you the same results.
• Instant Espresso Powder. Enhances the flavor of the chocolate.
• Baking Soda + Baking Powder. Leavening agents.
• Salt. Balances the sweetness.
• Eggs. Gives the cake structure and moisture, as well as a lighter texture.
• Sour Cream + Whole Milk. The fat in the sour cream and milk makes for a tender, moist and flavorful cake.
• Vegetable Oil. Moisture.
• Vanilla Extract. Flavor.
• Chocolate. You’ll need either chocolate chips or a couple bars of chocolate to make the ganache.
• Cream. Be sure to use heavy whipping cream for a rich, creamy ganache.

Instructions

Cake

• Preheat the oven to 350 F, and position a rack in the center of the oven.
• Prep a 9×13 inch baking pan by spraying it with non-stick baking spray if you plan on serving the cake from the pan. Or, if you plan on turning the cake out of the pan onto a serving platter, you’ll need to line it with a sheet of parchment baking paper, to ensure the cake comes out cleanly.
• In a large bowl, sift together the flour, sugar, cocoa powder, espresso powder, baking soda, baking powder and salt.
• In a separate bowl, whisk together the eggs, sour cream, milk, oil and vanilla, until well combined. Add the wet ingredients to the dry, and whisk the batter just until combined.

• Pour the batter into the pan. Bake the cake for about 38-42 minutes, until the center springs back when lightly touched, and a toothpick or cake tester inserted in the center comes out clean. (The top/center of the cake might look a little wrinkly or puckered, which is totally normal for this recipe.)
• Set the pan on a cooling rack, cover loosely with a clean kitchen towel, and let cool for about an hour (or cool completely to room temperature) before frosting with the ganache. If turning the cake out onto a serving platter, place the platter on top of the pan, and carefully flip the platter and pan over, letting the cake fall out onto the platter. Peel the parchment paper off the cake. Keep the cake covered with a towel until you’re ready to frost the cake.

TIP: It’s fine to spread ganache onto a cake that’s still warm. If you’re frosting your cake with buttercream, however, your cake must be completely cooled first.

Ganache

• While the cake is cooling, you can start on the ganache. Finely chop the chocolate (no bigger than 1/4 inch pieces), and scrape the chocolate into a bowl.
• In a saucepan, heat the cream over medium heat, just until hot and beginning to simmer around the edges.
• Pour the hot cream over the chocolate, let sit for 3 minutes, then stir with a spatula until it smooths out into a creamy ganache.

TIP: You can also make the ganache over a double boiler. Simply combine both the chocolate and cream in a heat proof bowl. Set the bowl over a saucepan of gently simmering water, making sure that the bottom of the bowl does not touch the water. Let the cream warm up and the chocolate melt, stirring with a spatula until smooth and creamy.

• Let the ganache cool at room temperature, stirring occasionally, until it’s thickened a little.
• Spread the ganache onto the cake.

• You can serve the cake warm, or you can wait several hours for it to cool completely and the ganache to set. Cut into 15 squares, by cutting the cake into thirds vertically and fifths horizontally.
• If you like, decorate the top of the cake with mini chocolate chips, chopped chocolate, or sprinkles.

Recipe Variations

Smaller Size. If a 9×13 pan of cake is too much cake for your family, just cut the recipe in half, and bake your chocolate sour cream cake in a 9 inch square baking pan for about 30 minutes, or until a cake tester comes out clean.

Make a Layer Cake. For a chocolate layer cake, see my best high altitude chocolate cake recipe for pan sizes and baking times.

Frost with Buttercream. If you want something sweeter than ganache, then frost your cake with fluffy buttercream frosting. You can pair chocolate cake with pretty much any flavor of frosting, and it would be fantastic. See my comprehensive post on perfect American buttercream for recipes, flavor variations and tips.

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

How long does it take the ganache to fully set?

As the melted chocolate re-solidifies, the ganache will thicken into a soft fudge-like consistency. It might take 3-4 hours to fully set. You can speed this up by placing the cake in the refrigerator for 30 minutes.

What kind of cocoa powder did you use?

I used Drost Dutch-processed Cocoa Powder for today’s chocolate sheet cake. I talk quite a bit about types of cocoa powders and other favorite brands in this chocolate cake recipe post.

Do I have to use the espresso powder?

I love adding instant espresso powder to chocolate cake, because it really intensifies and complements the flavor of the cake, without making it taste like coffee. I use Medaglia D’Oro Instant Espresso Coffee, which I buy at my local grocery store. Many people make my chocolate cake recipe without the espresso powder, though.

How should I store the leftover chocolate sheet cake?

Keep the leftover cake in an airtight container at room temperature for up to 3-5 days. You can also gently rewarm leftover pieces of cake for 30-40 seconds at 50% power in the microwave.

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