grease a springform and powder with flour, peel the apple and cut them in half, remove the core, cut them in top (not slicing), then pour them with lemon juice (avoids getting them brown)
heat the oven to 175* (E-oven). Stir butter, sugar, vanilla-sugar and a pinch of salt with egg beater creamy. Mix the eggs one by one in. Stir flour and baking powder short under the mixture.