Warm the eggs (for example, place in a bowl with warm water) or remove from the refrigerator earlier. Gently heat the milk or bring to room temperature.
Preheat the oven to 220°C, and also preheat an ovenproof dish or ovenproof skillet or another form such as a tart pan, diameter about 20 cm, in the middle of the oven.
Clarify 4 tablespoons of butter (heat in a saucepan, collect and remove the foam). Peel the apple and cut into 8-10 pieces (slices).
Place eggs in a blender (standing, with pitcher), add milk, flour, vanilla sugar and salt.
Mix the ingredients from the blender briefly (4 seconds) into a smooth batter.
Pull out the oven rack with the heated dish, pour 2 tablespoons of clarified butter, then slowly pour the mixed ingredients over it as an omelet. Arrange apple pieces and close the oven.
Bake uncovered for about 20 minutes, until the omelet rises in places and is nicely browned and crispy.
Remove from the oven, sprinkle with cinnamon. Serve with the remaining clarified butter and powdered sugar.
