Place the puff pastry slices next to each other and allow to thaw. Wash, stalk and stone the cherries
Roll out puff pastry slices separately in a rectangular shape on a floured work surface (1 24 x 10 cm, the other approx. 28 x 13 cm). Place the puff pastry on a baking tray lined with baking paper and prick a few times with a fork (not too much, otherwise the pastry will not rise). Bake the puff pastry in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 15-20 minutes until golden brown. Take out and let cool on a cake rack
Simmer 100 ml cherry nectar, 2 tablespoons sugar and cherries for about 4 minutes. Mix starch and 50 ml nectar until smooth and stir into the cherries with a wooden spoon. Simmer the cherries for about 1 minute, then remove from heat and allow to cool, stirring occasionally
Line the box form (base measured approx. 10 x 24 cm) with foil. Place a small slice of puff pastry on the base, cut it into small pieces if necessary. Spread the cherries on top and chill
Soak gelatine in cold water. Mix sour cream, 50 g sugar and vanillin sugar. Squeeze the gelatine and melt it in a small pot. Stir in 3 tbsp. cream, then stir into the rest of the cream. Chill the cream for about 15 minutes until it starts to gel
Whip the cream until stiff and fold into the cream. Spread the cream on the cherries and finish with the 2nd slice of puff pastry. Chill the cake for at least 4 hours
waiting time approx. 4 1/3 hours