Boil 450 ml milk. Stir sauce powder, sugar and 50 ml milk until smooth. Stir into the boiling milk, bring to the boil and simmer for 1 minute while stirring. Remove from the stove. Let cool while stirring several times
Wash apples and grate them dry. Cut a lid off the apples. Hollow out apples with a ball cutter so that only a narrow edge remains. Drizzle apples with lemon juice
Fill approx. 5 tablespoons of red fruit jelly into each apple. Put the apples into an ovenproof dish and bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 35 minutes
In the meantime, place puff pastry slices next to each other on a floured work surface and allow to thaw for 10-15 minutes, then roll out 4 grids with a dough roller. Place 1 puff pastry slice over 1 apple lid and cut off at the edges, slightly overlapping. Put the apple lids into the tin halfway through the cooking time
Arrange baked apples and vanilla sauce on plates and serve warm. Serve with the rest of the red fruit jelly