Place the puff pastry slices next to each other and allow to thaw. Stir mascarpone, lemon juice, 1 tablespoon sugar and vanillin sugar until smooth. Roll out puff pastry slices (20 x 30 cm). Halve the slices (15 x 20 cm) and spread the puff pastry with mascarpone, leaving an approx. 1 cm wide edge. Mix cream and egg yolks. Spread the egg-cream on the free edge and sprinkle with brown sugar. Place the tartes on a baking tray lined with baking paper and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 16-20 minutes.
Wash apricots hot and dab dry. Halve the apricots, remove stones and cut the flesh into slices. Caramelise 50 g sugar in a pan and add 4 tbsp. water.
Bring the caramel to the boil and simmer the apricots in it over a low heat for about 3 minutes and remove. Take the tartes out of the oven and spread the apricots on top. Let the tartes cool down, arrange on plates and sprinkle with the rest of the caramel. Serve with vanilla ice cream.