Preheat oven to 350°F. Line two 9-inch or 8-inch cake pans with circles of parchment paper in the bottoms and spray the sides. Set aside.
Whisk the flour, baking soda, cocoa powder, and salt together in a large bowl. Set aside.
3 cups cake flour, 1 teaspoon baking soda, 3 Tablespoons unsweetened cocoa powder, ½ teaspoon salt
Beat the butter and sugar together on high speed for 3-4 minutes in the bowl of a stand mixer with a paddle attachment until light and creamy. Add the oil and mix again, scraping the sides of the bowl.
½ cup salted butter, 2 cups granulated sugar, 1 cup vegetable oil
Add eggs, one at a time, and vanilla, beating on medium-high speed between each addition until combined. Add vinegar and food coloring, using as much food coloring as needed to get the desired color.
3 large eggs, 1 Tablespoon vanilla extract, 1 Tablespoon distilled white vinegar, 2 Tablespoons red liquid food coloring
Turn mixer to low speed and add the dry ingredients alternately with the buttermilk in 2-3 additions, mixing just until combined between each addition and scraping the bottom and sides of the bowl as needed.
1 cup buttermilk
Transfer batter to the prepared pans and bake for 30-35 minutes (for 9-inch pans) or 38-43 minutes (for 8-inch pans) until a cake tester inserted in the center comes out clean with just a few crumbs. Do not overbake. Remove from oven and cool completely.