In a large mixing bowl combine: the flour, cocoa powder sugar, baking powder, baking soda, and salt. Mix well.
Melt the butter in the microwave and allow a few minutes to cool.
Measure out 1 cup of milk into a measuring cup with space to add 1 cracked egg. Mix well to combine. Once the butter has cooled a bit, add it as well.
Make a well in the center of the dried ingredients and pour in the wet ingredients.
Mix it all together until it is just combined and there is no dry flour. Don't worry about it being lumpy, the lumps will cook out. You don't want to overmix the batter.
Allow the batter to sit out while the waffle maker heats up. The batter will thicken some as the flour hydrates. I would let the batter sit for about 5 minutes at least.
Once the waffle maker is hot. Brush butter on both top and bottom of the waffle maker then add your batter. Cook until waffle can be easily removed without sticking and it appears completely set. Repeat this until you have cooked all the waffles.