Preheat oven to 350°F. Grease and lightly flour 2 cupcake pans (24 cupcakes).

To make the batter: In a small bowl, sift the cake flour and set aside. In a large bowl, on the medium speed of an electric mixer, cream the butter and sugar until very light and fluffy, about 5 minutes. Add the eggs, one at a time, beating well after each addition. In a small bowl, whisk together the red food coloring, cocoa, and vanilla. Add to the batter and beat well.

In a measuring cup, stir the salt into the buttermilk. Add to the batter in three parts alternating with the flour. With each addition, beat until the ingredients are incorporated, but do not overbeat. In a small bowl, stir together the cider vinegar and baking soda. Add to the batter and mix well. Using a rubber spatula, scrape down the batter in the bowl, making sure the ingredients are well blended and the batter is smooth.

Divide the batter among the prepared pans. Arrange the oven racks in the upper and lower thirds of the oven and bake the cupcakes, switching positions of the pans halfway through baking, until a tester comes out clean, about 20 minutes. Cool the cupcakes in the pan 10 minutes, then remove from the pan and cool completely on a rack before icing. To ice, mound about ¼ cup of frosting on top of each cupcake and use an icing spatula to make a swirl on top. If desired, decorate with colored sprinkles.