1. 1. Prepare your baking dish and oven: Preheat your oven to 375 F (190 C). Lightly grease an 8×8 inch baking dish with butter or cooking spray. This prevents sticking and ensures easy removal of the bake.

2. 2. Combine dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps, creating a uniform mixture.

3. 3. Mix wet ingredients: In a separate medium bowl, whisk together the sourdough starter discard, milk, 1/4 cup melted butter, egg, and vanilla extract until well combined and smooth.

4. 4. Combine wet and dry mixtures: Pour the wet ingredient mixture into the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will result in a tender bake.

5. 5. Fold in the apples: Gently fold the diced apples into the batter. Distribute them evenly throughout the mixture so every bite gets some apple goodness. Pour the batter into your prepared 8×8 inch baking dish and spread it evenly.

6. 6. Create the cinnamon-sugar topping: In a small bowl, mix the ground cinnamon and brown sugar together. Sprinkle this mixture evenly over the top of the batter in the baking dish. Drizzle the remaining 2 tablespoons of melted butter over the cinnamon-sugar topping.

7. 7. Bake until golden: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean. The top should be golden brown and the apples tender.

8. 8. Prepare the glaze and serve: While the bake cools slightly, whisk together the powdered sugar and 1-2 tablespoons of milk or water in a small bowl until you have a smooth, pourable glaze. Drizzle the glaze over the warm breakfast bake just before serving.