Grease a tart mould (26 cm Ø) with lifting base and dust with flour. Rinse lemon hot and dab dry. Cut off a piece of peel and put aside. Finely grate the remaining peel.
For the dough 250 g flour, icing sugar, 1 vanilla sugar, grated lemon peel, 1 pinch of salt, egg, 1 tablespoon of cold water and 125 g butter in pieces, first with the dough hooks of the mixer, then briefly knead with your hands to a shortcrust pastry.
Roll out the dough on a lightly floured piece of baking parchment round (approx. 30 cm Ø). Use the paper to turn over into the tin. Remove the paper. Press the dough at the edge approx. 1⁄2 cm above the edge of the tin.
Prick the pastry base more often with a fork. Chill for about 30 minutes.
For the berry sauce, wash, clean and halve the strawberries. Select the remaining berries, wash and drain if necessary. Squeeze half the lemon. Preheat the oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see
manufacturer). Boil up the nectar, 50 g sugar, lemon juice and lemon peel. Mix sauce powder with 75 ml cold water until smooth. Stir into the hot nectar. Simmer while stirring for at least 1 minute. Fold in the berries.
Let it cool down and stir more often.
Bake the tart in a hot oven on the lowest shelf for 25-30 minutes. Remove from the oven and leave to cool in the mould for about 10 minutes. Carefully remove from the mould and let it cool down.
Whip the sour cream, 30 g sugar and 1 vanilla sugar with the whisks of the mixer. Spread in the tart base. Add the berry coulis.