Preheat oven to 350˚F. Line (or butter) muffin tin.
In a measuring cup, warm buttermilk (or milk with vinegar or lemon juice) in microwave. Whisk in oil and egg.
In a mixing bowl, mix together sugar, all purpose flour, whole wheat flour, cocoa powder, baking powder, and baking soda.
Add the wet ingredients to the dry and beat or whisk well.
Mix in very hot water. The mixture will be quite runny.
Pour into muffin tins.
Bake at 350˚F for ~25 minutes, until cupcake tops are springy to the touch. Do not overcook. As soon as possible, transfer the muffins to a rack. Allow to cool while making icing (if making Ermine Icing, I usually start it while the cupcakes are baking since it requires cooling time too)!