Beat butter until thick and creamy, separate eggs, vanilla sugar, egg yolks, sugar also beat until thick and creamy. Mix both together thoroughly. Stir curd and cinnamon until smooth and stir into butter/egg yolk mixture. Whip egg whites until stiff and fold in. Mix hazelnuts, crumbled onions and 1 tbsp. sugar. Drain the morello cherries. Butter a microwave-safe, wide, shallow dish. Pour in half of the curd mixture, then in order half of the crumbs, the cherries, the remaining curd and the remaining crumbs. Cook at 600 watts – covered for 5 minutes, then open for 15 minutes. After switching off, leave in the oven for another 2 to 3 minutes (temperature equalization).
Serve dusted with powdered sugar.