Combine in a mixing bowl:
2 cups flour
2 cups sugar
1/4 teaspoon salt

In a saucepan, melt:
2 sticks butter
Add 4 heaping tablespoons cocoa. Stir together.
Add 1 cup boiling water, allow mixture to boil for 30 seconds, then turn off heat. Pour over flour mixture, and stir lightly to cool.

In measuring cup, pour 1/2 cup buttermilk.
Add:
2 beaten eggs
1 teaspoon baking soda
1 teaspoon vanilla

Stir buttermilk mixture into butter/chocolate mixture.

Pour into sheet cake pan* and bake at 350-degrees for 20 minutes.

*I have also used this recipe to make 2 dozen cupcakes (same baking time).

Source: The Pioneer Woman