Peel and quarter the sour apples, then slice them thinly. Toss with cinnamon to taste.
Separate the 6 eggs into yolks and whites in separate bowls.
Mix the egg yolks with the honey until well combined.
In another bowl, mix the baking powder with the semolina.
Combine the egg yolk-honey mixture, the baking powder-semolina mixture, and the quark until smooth and well blended.
Beat the egg whites until stiff peaks form, about 3 to 5 minutes with an electric mixer.
Fold the beaten egg whites gently into the quark mixture in 2 to 3 additions until just combined.
Layer the quark mixture and apple slices alternately in a baking dish, starting and ending with the quark mixture.
Bake in a preheated oven at 170 °C (338 °F) on conventional heat (top and bottom elements) for 45 minutes until the top is golden brown and the casserole is set.