In a small skillet over medium heat, melt 1 tablespoon butter. Add diced apple, brown sugar, and ½ teaspoon cinnamon. Cook for 5–7 minutes until tender and caramelized. Set aside to cool slightly.

In a mixing bowl, whisk together flour, sugar, baking powder, baking soda, cinnamon, and salt.

In a separate bowl, mix buttermilk, egg, melted butter, and vanilla. Pour the wet mixture into the dry and stir until just combined. Fold in the apple mixture gently.

Preheat and lightly grease a waffle iron. Spoon batter into the center of each mold. Close and cook for 3–4 minutes or until golden brown and cooked through. Remove and cool on a wire rack.

Whisk powdered sugar, milk, and vanilla together until smooth. Adjust thickness with more milk or sugar if needed.

Once waffle donuts are warm (not hot), dip tops into glaze or drizzle with a spoon. Let set before serving.