Make waffles: Stir together flour, sugar, cocoa, baking powder, and salt in a large mixing bowl. Stir in milk, eggs, and butter until the mixture is smooth.
Make hard sauce: stir together softened butter, confectioners' sugar, vanilla extract, and milk. Sauce should be fairly stiff. Set aside.
Spray preheated waffle iron with nonstick cooking spray. Pour waffle mix onto hot waffle iron. Cook until golden brown.