Grease a fat pan (approx. 32 x 39 cm; approx. 3.5 cm deep). For the crumble dough, melt butter at low heat and let it cool down for about 5 minutes. Mix flour, sugar, vanillin sugar, salt and Citro-Back. Knead the liquid butter gradually with the dough hooks of the hand mixer. Cover the dough and leave to cool for approx. 30 minutes
Peel, halve and core apples. Make several longitudinal incisions on the curved side or carve deeply with a fork. Sprinkle apples with 3 tbsp. lemon juice
Spread 2/3 of the crumble as a base on the fat pan and press on. Place the apple halves on top with the curvature facing upwards. Spread the remaining crumbles on top. Bake in the preheated oven (electric cooker: 200 °C/circulating air: 175 °C/gas: level 3) for approx. 55 minutes. Let them cool down
Mix icing sugar and 1-2 tablespoons lemon juice. Spread in strips on the cake. Leave to dry