In a medium bowl, cream together the 1/2 cup butter and white sugar until light and fluffy. Add in the eggs one at a time and beat together until fully combined.
In a separate bowl, mix together the flour, cocoa powder, salt, baking powder and baking soda.
In a small bowl, mix together the coffee and the milk.
Alternate between mixing in the dry ingredients and the milk mixture into the wet ingredients until fully incorporated.
Scoop the batter into the prepared muffin pans so that each cup is 3/4 full. Place in the preheated oven and bake for 15-20 minutes, or until a toothpick inserted in the centre comes out clean.