Read your waffle maker's instructions and pre-heat it accordingly.
In a bowl, whisk together the melted butter, milk, and egg until fully combined. Then, add the brown sugar and stir to mix and dissolve it.
5 Tbsp Butter, 1½ Cups Milk, 1 Egg, 2 Tbsp Brown Sugar
In another bowl, combine the flour, baking powder, and cinnamon, stir together and set aside.
2 Cups Flour, 2 Tsp Baking Powder, 1 Tsp Cinnamon
Grate your apple and use paper towel to get much of the moisture out of it. You don't need to go overboard, but you want it mostly dry to handle.
1 Cup Shredded Apple
Make a well in the dry mix and pour the wet mix into it, stirring it all into a batter until it just comes together. Don't worry about a few lumps. Then, fold in the shredded apple.
Grease or spray your waffle iron as instructed, add however much batter your machine calls for, and cook according to the instructions. Usually, that means about 3-5 minutes per waffle, and this recipe makes about four large waffles.