Preheat the oven to 350F degrees. Line a muffin pan with muffin papers.
In a large bowl sift together the cake flour, cocoa and salt. Whisk gently.
In a separate large bowl beat the butter until fluffy (about 2 minutes). Then beat in the sugar until creamy (about 1-2 more minutes).
Beat in the egg and vanilla extract.
In a liquid measuring cup whisk together the buttermilk and red food coloring.
Beat the dry ingredients (flour mixture) into the butter mixture about ⅓ at a time, alternating with about ⅓ of the buttermilk mixture. Turn off the mixer and scrape down the sides of the bowl as needed.
In a small bowl or cup dissolve the baking soda into the vinegar. Quickly beat it into the cupcake batter.
Spoon the batter into the prepared muffin papers, filling each about ⅔ full. Bake in the preheated oven for 15-18 minutes, or until an inserted toothpick comes out clean. Allow the cupcakes to cool in the pan for 5-10 minutes, before removing from the pan and continuing to cool on a wire rack.