Cake:

1 cup flour
1 cup sugar
1/8 tsp. salt

  • Mix together in large bowl

1 egg, beaten
1/4 cup buttermilk
1/2 tsp. baking soda
1/2 tsp. vanilla

  • In a small bowl, beat the egg, then mix in other ingredients.
  • Add to dry ingredients.

4 Tbsp. unsalted butter
4 Tbsp. cocoa powder
1/2 cup boiling water

  • Melt butter, then stir in cocoa powder and water, then add to batter.
  • Pour batter into greased quarter sheet pan (10” x 12”).
  • Bake at 350°F for 15-18 minutes, until a toothpick comes out clean.

Frosting:

7 Tbsp. unsalted butter
4 Tbsp. cocoa powder
3 Tbsp. buttermilk
1 tsp. vanilla
2 cups powdered sugar

  • Melt the butter, then stir in cocoa powder, buttermilk, and vanilla.
  • Remove from heat and whisk in powdered sugar.
  • Pour over cake just after removing from the oven.
  • Let cool at least 30 minutes before serving.

Source: https://www.dessertfortwo.com/texas-chocolate-quarter-sheet-cake/