Butter a square baking dish or 4 smaller molds. Preheat the oven to 180 ° C (top / bottom heat).
First prepare the crumble. Melt the butter for this. Mix the flour, sugar, salt and vanilla sugar and fold in the melted butter and egg yolks with a fork.
Peel, core and quarter the apples. Cut the quarters into slices and mix immediately with the lemon juice. Mix in the sugar as well.
Pour the apple mixture into the mold and distribute evenly. Sprinkle the crumble on top and bake in the oven for 35 minutes.
A dab of whipped cream, vanilla ice cream or vanilla sauce goes well with it.