Preheat the oven to 350ºF.
In a small bowl, sift together the cake flour, baking soda, salt and cocoa powder. Set aside.
Cream together the butter and sugar then beat in the eggs one at a time.
Add in the vanilla.
Beat in the sifted flour mixture alternately with the buttermilk.
Add in the food coloring and blend until well mixed. Then stir in the mashed raspberries.
Scoop the batter into cupcake tins lined with cupcake cups.
Bake for 22-24 minutes, rotating the cupcake tin in the oven halfway through.
Remove and let cool before frosting with cream cheese frosting (recipe below).