Preheat oven to 350°F. Grease and flour two 9-inch round cake pans.

In a large bowl, combine flour, sugar, cocoa powder, and baking soda.

Add buttermilk, vegetable oil, and vanilla to the dry ingredients. Mix until smooth.

Gradually add boiling water, mixing continuously. The batter will be thin.

Pour batter evenly into prepared pans and bake for 30 minutes or until a toothpick inserted into the center comes out clean.

Allow cakes to cool in pans for 10 minutes, then turn out onto wire racks to cool completely.