Preheat the oven to 180 °C.
Mix the liquid cooled butter with the sugar, eggs, vanilla flavoring and buttermilk.
Mix well the flour, cocoa and baking powder. Mix this mixture into the butter and egg mixture alternately with the chocolate milk. Finally, stir in the chocolate chips.
Pour the batter into muffin tins and bake the muffins for about 20 minutes.