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Chocolate Sheet Cake

Prep Time 15 minutes
Cook Time 25 minutes
Total Time 40 minutes
Author GlutenFreeBaking.com

Ingredients

For the Cake

  • 2 cups granulated sugar (14 ounces; 396 grams)
  • 1 cup finely ground white rice flour (4 ounces; 113 grams)
  • 1/2 cup sweet rice flour (2 ounces; 56 grams)
  • 1/2 cup cornstarch (2 ounces; 56 grams)
  • 1 teaspoon baking soda
  • 1/4 teaspoons salt
  • 2 sticks unsalted butter (8 ounces; 226 grams)
  • 5 tablespoons natural cocoa powder (about 1 ounce; 26 grams)
  • 1 cup boiling water (8 ounces; 226 grams)
  • 1/2 cup buttermilk (4 ounces; 113 grams)
  • 2 large eggs (3 1/2 ounces; 100 grams
  • 1 teaspoon vanilla extract

For the Icing

  • 1 3/4 sticks butter (7 ounces; 198 grams)
  • 3 1/2 cups powdered sugar (14 ounces; 396 grams)
  • 5 tablespoons natural cocoa powder (about 1 ounce; 26 grams)
  • 6 tablespoons milk (3 ounces; 85 grams)

Instructions

  1. Make the Cake: Preheat oven to 350 degrees F. Grease a 12x18x1 pan with nonstick cooking spray. Set aside.

  2. Whisk together granulated sugar, white rice flour, sweet rice flour, cornstarch, baking soda, and salt.  

  3. Melt the butter over medium heat in a small saucepan over medium heat. Add cocoa powder and stir to combine. Reduce heat to low and allow mixture to cook for 3 minutes. Stir in boiling water and cook for 30 seconds. Remove from heat and allow to cool for 30 seconds.

  4. Pour mixture over dry ingredients. Stir to combine. (You can use a balloon whisk for this.) Blend until smooth. Add buttermilk, eggs, and vanilla. Mix until a batter forms. Pour batter evenly into prepared pan.

  5. Bake for 25 minutes or until cake springs back to the touch. Remove cake from the oven.

  6. Make the Frosting: Melt butter in a small saucepan over medium heat. Add cocoa powder. Stir to combine. Turn off heat. Add the powdered sugar, milk, and vanilla. Stir until smooth. Pour over warm cake.