Preheat your oven to 350°F (180°C) and grease and flour two 9-inch round cake pans.
In a medium bowl, sift together the cake flour and cocoa powder. Set aside.
2 tablespoons unsweetened cocoa powder, 2 1/2 cups cake flour
In a large mixing bowl, cream together the butter, oil, and sugar until light and fluffy.
1 cup butter, 1/4 cup oil, 1 1/2 cups granulated sugar
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
2 eggs, 1 teaspoon vanilla extract
In a small bowl, whisk together the buttermilk, red food colouring, and vinegar.
1 cup buttermilk, 1 tablespoon red food coloring, 1 teaspoon distilled white vinegar
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk mixture, starting and ending with the dry ingredients. Mix until just combined.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.