Preheat the oven to 350°F (175°C).
Grease two 9-inch round cake pans and line the bottoms with parchment paper.
In a large bowl, sift together the flour, cocoa powder, baking soda, and salt.
In another bowl, cream the softened butter and sugar until light and fluffy.
Add the eggs, one at a time, and mix until well combined.
Stir in the Kahlua and vanilla extract until blended.
Alternate adding the dry ingredients and buttermilk to the butter mixture, beginning and ending with the dry ingredients.
Divide the batter evenly between the prepared pans.
Bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for 10 minutes before transferring to a wire rack.
Frost with your favorite frosting once completely cooled.
