Preheat the oven to 200°C (top and bottom heat) or 180°C (fan oven). Wash the apple, core it, and cut it into small, thin slices.

Place the applesauce, eggs, agave syrup (or honey), and cinnamon in a bowl and mix well. Add the rolled oats, raisins, baking powder, and milk, and stir carefully. Then fold in the apple pieces.

Grease a roughly 20 x 20 cm baking dish or brownie pan with a little oil or butter and spread the batter evenly in it, smoothing the surface. Sprinkle nuts over the top and bake at 200°C for 30 minutes, or until golden brown.

Remove the baked oatmeal from the oven and let it cool completely. Then cut the baked oatmeal into 4 equal pieces and pack them in a food storage container or similar, then refrigerate. This way, the baked oatmeal can be kept for up to a week. Enjoy the apple baked oatmeal cold in the morning or reheat each portion in the microwave for 60 to 90 seconds.

Add milk, protein powder, and starch to a shaker (such as a protein shaker or dressing shaker) and shake until smooth. Alternatively, simply put everything in a small blender and blend briefly.

Pour the protein mix into a small saucepan and heat over medium heat, stirring constantly, until the sauce has thickened slightly and reached the typical consistency of custard, about 3 to 5 minutes. Remove the pan from the heat and serve the custard with the apple baked oatmeal.