Classic Yellow Sheet Cake with Chocolate Buttercream Frosting

Soft yellow cake baked in a 9×13 sheet pan, frosted with rich, silky chocolate buttercream and finished with a generous shower of rainbow sprinkles — this cake is perfect for birthdays, gatherings, or any celebration.

This classic combination is an essential recipe to have in your baking collection. My husband often requests it for his birthday, and I happily oblige because it’s delicious and surprisingly easy. It’s also one of the happiest-looking cakes you can make.

This post is part of my sheet cake series — so far I’ve shared five different sheet cakes and I’ll be sharing more. Sheet cakes are a fun way to change up your decorating approach while keeping things simple and crowd-pleasing.

Let’s jump into this classic yellow sheet cake with chocolate buttercream. Below you’ll find what you need to know to bake and decorate it.

Ingredients for a classic yellow cake

This is a doctored cake mix recipe using a boxed yellow cake mix plus five simple additions. It’s a reliable way to get tender, flavorful cake without the precision required for some from-scratch recipes. Professional bakers often use similar methods to produce consistent results.

• Buttermilk – room temperature
• Sour cream – room temperature
• Eggs – large, room temperature
• Vegetable oil
• Vanilla
• Yellow cake mix – one 15.25 oz box (Duncan Hines recommended)

You don’t need a stand mixer for the cake batter — a whisk and a bowl will do. Combine the wet ingredients, sift in the cake mix, stir until smooth, then pour into a prepared 9×13 pan and bake.

What 9×13 cake pan is that?

I used a heavy-duty OXO 9×13 pan for this cake, but a glass pan or any similar-sized pan will work fine. Grease and flour or use baking spray before adding the batter.

Can I make the batter into other cakes?

Yes. This batter is very versatile:

Three 6-inch layers: Use the batter for stacked 6″ layers.

Two 8-inch layers: Divide and bake in 8″ pans.

Bundt cake: Bake a little longer and test with a toothpick.

Cupcakes: Makes about 24 cupcakes; bake 12–15 minutes.

This recipe appears in my Cake Confidence cookbook and I’ll Bring the Cake cookbook in alternative formats such as a 6″ round.

Where can I find those sprinkles?

I usually buy rainbow sprinkles in bulk, but you can also find them at most grocery stores in the baking aisle. Use a full cup for a festive finish.

How to make chocolate buttercream

This chocolate buttercream combines both cocoa powder and melted chocolate for depth and richness. The method below yields a silky, spreadable buttercream that’s easy to pipe or frost with a spatula.

Make the ganache: Heat the chocolate and heavy cream together in short bursts in the microwave, stirring each time, until fully melted and smooth. Cool to near room temperature.

Whip the butter: In a stand mixer with the paddle attachment, beat softened butter until light and fluffy (about 1 minute). Add salt, vanilla, and cocoa powder, then mix in the cooled ganache.

Add powdered sugar: With the mixer on low, add powdered sugar a little at a time until combined. If the buttercream is too thick, add heavy cream one teaspoon at a time until you reach desired consistency.

Finish: Increase the mixer speed to high and whip the buttercream for 1–2 minutes to lighten its texture and color. Hand-beat briefly with a wooden spoon to remove any large air bubbles. If piping, transfer buttercream to piping bags; otherwise, spread with an offset spatula and add sprinkles.

What piping tips are needed for this design?

For the decoration shown I used a Wilton 127D and a large French tip (Ateco 869). You’ll also want disposable or reusable piping bags to hold the buttercream.

Video of the decorating process

I love seeing your Baking with Blondie creations — tag @bakingwithblondie and use #bakingwithblondie so I can see your cakes!

Happy baking!

xo, Mandy