For the dough, knead flour, 100 g butter in pieces, 50 g sugar, 1 pinch of salt and 2 tablespoons cold water first with your hands, then quickly with the dough hooks of the mixer to a smooth dough. Wrap in foil and chill for about 1 hour.
Wash, halve and stone the plums and, depending on size, cut them in half or into wide slices. Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Mix mascarpone, egg yolk and vanilla sugar.
Coarsely chop 1 tablespoon of almonds, grind the remaining almonds finely.
Roll out the dough between two layers of baking paper (approx. 3 mm thin; approx. 30 cm Ø). Pull the paper onto a baking tray and remove the upper paper. Sprinkle ground almonds on the dough, leaving a rim of about 5 cm wide.
Spread the mascarpone cream on the almonds. Place plums on top. Put a little bit of the dough edge over the plums. Sprinkle 2 tablespoons of sugar and chopped almonds over the plums. Spread 2 tablespoons of butter in flakes on top.
Bake the crostata in a hot oven on the middle shelf for 25-30 minutes until golden brown. Serve with vanilla ice cream.