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Classic Yellow Sheet Cake with Chocolate Buttercream and Sprinkles

Print Recipe
Soft tender yellow cake with mouthwatering chocolate buttercream - topped off with all the rainbow sprinkles and ready to party!
Servings 20 servings (more or less, depending on how you slice it)
Author Mandy Merriman, Baking with Blondie

Equipment

  • Wilton 127 D Piping Tip
  • Large French Piping Tip
  • 9x13 Baking Pan

Ingredients

Classic Yellow Cake

  • 3/4 cup buttermilk room temperature
  • 2/3 cup sour cream room temperature
  • 3 whole eggs room temperature
  • 1/3 cup vegetable oil
  • 1 Tablespoon vanilla
  • 1 15.25oz Yellow Cake Mix (I used Duncan Hines)

Chocolate Buttercream

  • 1 cup Ghirardelli chocolate melts or chocolate chips
  • 1/2 cup heavy cream
  • 1 1/2 cup (or three sticks) unsalted butter left out at room temperature for 10-15 minutes
  • 1 pinch salt
  • 1 Tablespoon vanilla
  • 1/4 cup cocoa powder
  • 7-8 cups powdered sugar

Extras

  • 1 cup rainbow sprinkles

Instructions

For the yellow cake:

  • Preheat the oven to 325 degrees. Prep the 9x13 sheet pan with shortening and flour, or baking spray. Set aside
  • In a large mixing bowl, whisk together all the ingredients except for the cake mix until they're all combined. Sift in the cake mix, then gently stir to fully combine (no pockets of powdered cake mix!). Pour into the prepared baking pan and spread evenly.
  • Bake for 25-27 minutes, then let cool completely before adding on the frosting.

For the chocolate buttercream:

  • Heat the chocolate and heavy cream in the microwave for 30 seconds, then stir. Repeat and stir until smooth. Let cool until the ganache is closer to room temperature.
  • In the bowl of a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy, about 1 minute. Add in the salt, vanilla, and cocoa powder. Add in the cooled ganache and whip up again. Scrape down the sides of the bowl, then add in the powdered sugar slowly until combined. (You may need to add in a little more heavy cream - start with 1 Teaspoon, and go from there).
  • Flip the stand mixer to the highest speed, and let whip up for 2 minutes until the buttercream has lightened in texture and color. Use a wooden spoon to hand-beat out the air bubbles, then add the buttercream to two piping bags with the piping tips indicated above if decorating like I did. If not, slather on the buttercream with an offset icing spatula and add on the sprinkles.
  • If using the piping tips, with the 127 D piping tip (wide end on the cake) pipe straight lines that slightly overlap to cover the cake. Use the large french tip to pipe a shell border around the outside rim, then add on the sprinkles. Enjoy!