Waffles using muffin mix! GENIUS! To turn the muffin mix into a waffle mix, follow the package directions but add an extra 1/3 to 1/2 cup of milk or water. The batter should flow slowly, like a thick pancake batter. For a 16-ounce box of muffin mix, add an extra 1/2 cup of liquid; for a 12- to 14-ounce box, add an extra 1/3 cup; and for a 20-ounce box, add just under 3/4 cup.