Chocolate Buttermilk Sheet Cake

This delicious chocolate buttermilk sheet cake also provides a lesson in the science behind cake baking!

Why does cake rise? What does buttermilk do for a cake?

Baking soda makes a cake rise, but it needs an acid to activate it so it can do its magic. When you combine baking soda with an acid, the two ingredients react to produce carbon dioxide, the gas that we exhale that also allows baked goods to rise. It’s the same idea as the classic baking soda and vinegar volcano — but instead of a fizzy eruption, we get a delicious cake at the end.

In this recipe, buttermilk provides the acid that activates baking soda, giving us carbon dioxide gas. Buttermilk is made by combining milk with bacteria cultures. The bacteria feed on lactose, a sugar present in milk, and produce lactic acid.

Once we bake the cake in the oven, the carbon dioxide that has been produced heats and expands, giving us a light, fluffy cake that has risen in size!

Recipe

Prep Time: 20-30 minutes

Cook Time: 20-30 minutes

Total Time: ~60 minutes

Yield: 12-16 servings*

*serving size: 1 slice

Materials

• Knife

• Cutting board

• Bowls

• Saucepan

• Hand mixer, standing mixer, or whisk

• Measuring cup and spoons

Cake

Ingredients

• 2 cups flour

• 2 cups sugar

• ½ cup butter (1 stick)

• ½ cup canola oil

• 4 Tbsp cocoa

• 1 cup water

• 2 eggs, beaten

• ½ cup buttermilk

• 1 tsp baking soda

• 1 tsp vanilla

• ~1 cup chopped nuts (optional)
  

Instructions

1. Preheat oven to 400 degrees.

2. Grease and flour 11 x 17 sheet cake pan.

3. Mix flour and sugar together in a large bowl.

4. Boil butter, canola oil, cocoa, and water in saucepan.

5. Pour butter mix over flour and sugar.

6. Add in eggs, buttermilk, baking soda, and vanilla. Mix until combined.

7. Pour cake batter into prepared pan.

8. Bake at 400 degrees for 20-30 minutes until toothpick comes out clean.

9. Top with frosting when it comes out of the oven (recipe below).

10. Sprinkle with chopped nuts (optional).

Frosting

Ingredients

• ½ cup butter (1 stick), softened

• 4 Tbsp cocoa

• 4 Tbsp cocoa

• ⅓ cup buttermilk

• Dash of salt

• 1 16 oz. box powdered sugar

• 1 tsp vanilla
  

Instructions

1. Soften butter in the microwave (~10-15 seconds).

2. Blend together butter, cocoa, buttermilk, and salt .

3. Use a hand mixer to blend in the powdered sugar and vanilla.

4. Pour frosting over top of cake when it comes out of the oven.