Begin by peeling, coring, and dicing the tart apples into small chunks—about half-inch pieces work best.

In a mixing bowl, whisk together your all-purpose flour, baking powder, baking soda, salt, ground cinnamon, and nutmeg.

In a separate bowl, whisk together the eggs, granulated sugar, brown sugar, buttermilk, melted butter, and vanilla extract until smooth.

Carefully pour the wet mixture into the bowl of dry ingredients and gently stir until just combined.

Lightly grease your waffle iron and preheat it according to the manufacturer's instructions.

Spoon ¼ cup of the batter onto the preheated waffle iron for each donut and cook for 3–5 minutes.

While the donuts are cooking, whisk together your powdered sugar, milk, and a splash of vanilla extract in a small bowl until smooth.

Once the donuts are cooked, remove them from the waffle iron and drizzle with the prepared glaze while they are still warm.