Preheat the oven to 350°F. Line 24 cupcake tins with baking papers. Sift together the flour, cocoa, baking soda, and salt. Set aside.

In the bowl of an electric mixer, cream together the butter and sugar until fluffy, about 3 minutes. Add the vanilla. Add enough food coloring to turn the mixture a deep red; beat to combine. Add the eggs, one at a time, beating well after each addition. Alternately add flour mixture and buttermilk, beginning and ending with the flour.

Fill each baking paper two-third full. Bake until a skewer inserted into the middle of a cupcake comes out clean, about 20 minutes.