Preheat the oven to 180°
In a large bowl soften the butter with a hand mixer. Then add the sugar and mix again until you get a light mixture.
Now you can add the egg and the vanilla extract and mix again.
In another bowl whisk together the flour, the salt, the baking powder and the cocoa powder, then add the dry ingredients to the butter mixture.
In a small bowl mix the buttermilk and the food coloring and pour onto the dough.
Aside, you should now mix the baking soda and the vinegar and add them to the dough.
Mix everything until you get an even dough.
Place cupcake cases into your cupcake mold and pour the dough up to 2/3 into the cupcake forms and bake for 25 minutes.
Let them cool 10 minutes in the mold before putting them on a baking rack.
