Mix the flour, salt, milk and sugar together. Separate the eggs, mix the yolks with the butter, stir into the flour mixture and make a smooth dough (add a little milk if necessary). Let the dough soak for 30 minutes.
Peel and core the apples and cut into thin wedges. Beat the egg whites until stiff and fold into the batter with the apple wedges. Put the dough in greased, fire-proof portion molds, if the dish is intended as a dessert, fill it as a main dish in a large baking dish.
Bake in the oven at 220 ° C for 25 minutes (stick test). Then sprinkle with powdered sugar and serve.