For the dough, separate the eggs. Cover the egg white and chill. Put 250 g flour, 80 g sugar, 1 pinch of salt, 200 g butter in pieces, egg yolk and poppy seeds in a bowl. First mix with the dough hooks of the mixer, then knead briefly with your hands to a shortcrust pastry.
Form into a flat brick. Cover and leave to cool for at least 1 hour.
For the filling, select the berries, wash and drain if necessary. Stir egg white and 25 g sugar briefly with a whisk. Stir in sour cream.
Briefly knead the dough and roll out round (approx. 32 cm Ø) on a lightly floured sheet of baking paper. Place a tart mould (24 cm Ø) upside down on the dough plate. Use a knife to cut a wavy edge all around the tin.
Lift off the mould, turn it over. Lift the dough sheet into the mould using the paper and press it gently into the mould (see fig. 2). Briefly knead the remaining dough again, roll out and form small circles (
with a perforated nozzle, 1-1 1⁄2 cm Ø)
Preheat oven (electric cooker: 180 °C/circulating air: 160 °C/gas: see manufacturer). Spread the sandy mixture on the tart base. Spread the berries on top. Place dough circles in the middle of the tart. Bake in a hot oven for about 45 minutes.
Remove from the mould and let it cool down in the mould. Carefully lift the tart out of the mould using the baking paper. Bring jam to the boil with 3 tbsp. water and drizzle over the tart.