Glorious Red, White, and Blue Cake

Heat oven to 350 °F. Butter two 9-inch round cake pans, then line bottoms with rounds of wax paper. Butter paper and dust pans with some additional flour, knocking out excess. Resift cake flour together with cocoa, baking soda, and salt into a bowl. Beat butter and sugar in a large bowl with an electric mixer (fitted with paddle attachment if using stand mixer) at medium-high speed until combined well, then add oil and beat until very pale and creamy, about 3 minutes. Add eggs, one at a time, beating well after each addition, and beat in food coloring, vinegar, and vanilla extract. Reduce speed to low and mix in flour mixture and sour cream mixture in batches, beginning and ending with flour mixture, and mixing until batter is smooth. Divide batter between pans (about 3 cups in each) and smooth tops. Rap pans on counter a couple of times to expel any air bubbles. Bake in middle of oven until a wooden pick comes out clean and cake begins to pull away from sides of pans, 25 to 30 minutes. Keep oven on. Cool layers in pans on racks 10 minutes, then run a thin knife around edge of pans. Invert layers onto racks and peel off wax paper. Cool layers completely.