For the dough, mix flour with baking powder and sift into a mixing bowl. Add the quark, milk, oil, sugar, vanilla sugar and salt. Use the hand mixer with dough hook on the highest setting to form a dough in about a minute (not too long, otherwise the dough will stick). Roll out the dough on a parchment-lined baking sheet.
Cover the dough with the apple wedges.
For the apricot cream, mix the apricot jam, butter and egg yolk well together. Beat the egg whites with the sugar until the snow is shiny. Fold the protein mixture into the apricot cream and spread it on the apples. Bake the baking sheet on the middle rack at 160-180 ° C (hot air) for about 20-30 minutes.
Let the cake cool down on the baking tray for about 10 minutes and then pull it onto a wire rack and let it cool down completely.