
Make the red velvet cake batter: In a medium bowl, whisk together the flour, cocoa powder, and salt. In another large bowl, cream the butter and sugar until light and fluffy. Mix in the sour cream, oil, vanilla extract, and eggs one at a time. Add red food coloring until evenly colored. Alternate adding dry ingredients and buttermilk, ending with dry ingredients. Stir in the baking soda and vinegar.