Plug in your waffle iron to heat it up.
Melt the butter in a small pan over low heat and let cool slightly as you prepare the rest of the waffle ingredients.
3 tablespoons unsalted butter
Whisk the flour, sugar, baking powder, and salt together in a large bowl.
1½ cups all-purpose flour, ¼ cup granulated sugar, 2 teaspoons baking powder, ⅛ teaspoon salt
In a small bowl, or in the measuring cup used to measure your milk, whisk together the milk and eggs until they are well blended.
1½ cups milk, 2 large eggs
Add the milk and egg mixture and the butter to the bowl with the dry ingredients and stir only until just combined. A few lumps are fine.
Add the apple, cheese, and onion and stir to mix, making sure to break up any clumps.
1 apple, ¼ cup grated cheddar cheese, ¼ cup caramelized onions
Make the apple waffles according to your waffle maker's instructions.