Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Add eggs, buttermilk, oil, and vanilla to the dry ingredients. Mix until smooth.
Gradually stir in boiling water until well combined. The batter will be thin.
Divide the batter evenly between the prepared pans and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Cool the cakes in pans for 10 minutes, then transfer to a wire rack to cool completely.