For the Wachau apricot-grape strudel, separate the eggs. Beat egg yolks with sugar, vanilla sugar and cinnamon until foamy. Beat egg whites until stiff and first mix with flour, custard powder and nuts before carefully folding the beaten egg whites into the yolk mixture.
Spread the strudel dough, brush well with melted butter and spread the filling on about two-thirds of the dough. Spread apricot pieces and grapes evenly on top.
Gently roll up the strudel and place it on a well-buttered or parchment-lined baking sheet with the folded seam facing down. Brush generously with melted butter and bake in an oven preheated to 180 °C for about 30 minutes until golden brown. Allow the Wachau apricot-grape strudel to cool and serve with freshly whipped cream.