First preheat the oven to 180 ° C top / bottom heat. Mix the milk, egg and maple syrup together. Mix the oat flakes with the other ingredients and place in the baking dish. Wash the apple, remove the core and cut into fine cubes, add to the oatmeal mixture with the blueberries. Pour the egg and milk glaze over everything and mix a little with a fork. Bake the oatmeal casserole for 30 minutes. Greek yogurt and fresh blueberries go well with it. Tastes both cold and warm.