Preheat the oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.
In a large bowl, sift together all dry ingredients: flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, buttermilk, vegetable oil, and vanilla extract to the dry ingredients. Mix for 2 minutes until smooth.
Slowly add the boiling water, mixing on low speed. The batter will be thin, which is normal.
Divide the batter evenly between the two cake pans and smooth the tops. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
Notes
For a more intense chocolate flavor, add the optional sour cream and instant coffee granules.