Knead oat flakes, flour, sugar, cinnamon and room-warm butter into crumbles. Fill apples into a baking dish. Sprinkle the crumble on top.
Bake at 180 °C (gas 2, convection oven 175 °C) for 30 minutes.
(Source) Essen & Trinken 10/95 Reader’s recipe by Brigitte Rollin, Berlin.