Cut the vanilla pods in half lengthwise and scrape out the pulp. Wash the plums, drain, halve and stone. Halve the halves again. Cook the plums, 50 g sugar, almond liqueur and the pulp of 1 vanilla pod in a pot at medium heat for about 30 minutes to a compote.
Mix the starch with 2 tablespoons of water, stir into the plum compote. Bring to the boil briefly. Fill the compote into a bowl. Let it cool down, cover with foil and put it in a cool place for about 1 hour.
Put flour, almonds, butter in flakes, salt, 125 g sugar, pulp of 1 vanilla pod and egg in a bowl. Knead first with the dough hooks of the hand mixer, then with your hands to a smooth short pastry.
Wrap dough in foil and chill for about 30 minutes.
Roll out 2/3 of the dough on a lightly floured work surface to a circle (approx. 30 cm Ø) approx. 5 mm thin. Using the dough roller, place the dough in a greased tart tin (26 cm Ø) dusted with flour.
Cut off excess dough, knead with the remaining dough and roll out again to a thickness of approx. 5 mm. Cut out 36 circles with a round serrated cookie cutter (approx. 4.5 cm Ø). Put the stewed plums into the tart tin, cover with the dough circles slightly overlapping.
Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 45 minutes. Remove and let cool on a cake rack. Carefully remove from the tin, place on a plate and dust with icing sugar.