Butter and flour 2 (9-inch) cake pans and line each pan with a round of parchment paper.
Whisk together the flour, cocoa powder, baking soda and salt in a small bowl
Cream the butter, sugar and oil in a stand mixer fitted with the paddle attachment until light and fluffy. Add the eggs, one at a time, scraping down the sides of the bowl and beat until incorporated. Beat in the vanilla, vinegar and food coloring.
Add the flour mixture to the batter in 3 batches alternating with the buttermilk, mixing well after each addition.
Divide the batter evenly between the prepared pans and bake for 30 to 40 minutes or until a wooden skewer inserted into the center comes out with a few moist crumbs.
Cool on a baking rack for 15 minutes before removing the cake from the pans. Let cool completely before frosting.