Preheat oven to 350°F. Grease and flour two 9-inch cake pans, line with parchment paper, and then grease and flour again.
Cream together the butter and sugar until light and fluffy. Add oil and eggs, one at a time, until incorporated. Mix in the food coloring, vinegar, and vanilla extract.
In a separate bowl, sift together the flour, cocoa powder, salt and baking soda.
Alternately add the dry ingredients and the buttermilk to the butter mixture, starting and ending with the dry ingredients. Beat until well blended.
Scrape the sides of the bowl and incorporate any unmixed batter, if necessary.
Divide the batter evenly between the two prepared pans. Tap the pans on the counter to ensure that there are no air bubbles.
Bake until a toothpick inserted in the center of the cakes comes out clean, about 25-30 minutes. Cool the cakes for at least 10 minutes on a wire rack before removing from the pans. Allow the cakes to cool completely before frosting.