Preheat oven to 350 degrees F (175 degrees C). Grease and flour two 9-inch round cake pans.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cocoa powder. Set aside.
In a large bowl, beat together the oil, sugar, eggs, buttermilk, food coloring, vinegar, and vanilla extract until blended.
Gradually add the dry ingredients to the wet ingredients and mix until just blended.
Divide the batter evenly between the two prepared pans.
Bake for 25 to 30 minutes in the preheated oven, or until a toothpick inserted into the center of the cake comes out clean.
Cool for 10 minutes in the pans before turning out onto wire racks to cool completely.
To make the frosting, cream together the butter and powdered sugar in a medium bowl. Beat in the milk until the frosting is light and fluffy. Frost the cooled cake.
Interesting Facts
Red Velvet Cake was first made in the early 1900s.
The original recipe called for mashed potatoes instead of buttermilk.
The red color of the cake comes from the reaction between the vinegar and cocoa powder.
Red Velvet Cake is usually frosted with a cream cheese frosting.