Preheat oven to 350°F. Grease and flour two 9-inch round baking pans.
In a large bowl, whisk together flour, sugar, cocoa, baking soda, baking powder, and salt.
Add eggs, buttermilk, oil, and vanilla. Beat on medium speed for 2 minutes.
Stir in hot water (batter will be thin). Pour batter evenly into prepared pans.
Bake for 30–35 minutes or until a toothpick inserted comes out clean.
Cool for 10 minutes in pans, then remove to wire racks to cool completely.
Frost with your favorite chocolate frosting or ganache before serving.