For the base, mix 150 g flour with 50 g sugar and 1 pinch of salt in a bowl. Grate butter directly into the flour on a coarse grater. Mix everything briefly with a wooden spoon. Stir sour cream, lemon juice and 4 tbsp. cold water until smooth, add to the flour mixture. Mix first with a spoon, then with your hands only briefly until all ingredients are combined. You should still see butter flakes in the dough. Wrap dough in foil. Chill for about 1 hour.
Clean, wash and cut the rhubarb into pieces. Mix pudding powder with 3 tablespoons of sugar. Stir with 5 tablespoons of nectar until smooth. Boil up the rest of the nectar and rhubarb, simmer for about 1 minute. Stir in the pudding powder and simmer for about 1 minute, stirring continuously. Remove from heat. Wash and clean the strawberries, cut them into pieces and add them to the compote. Let them cool down.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Line a baking tray with baking paper. Roll out the dough round (approx. 34 cm Ø) on a floured work surface. Place on the baking tray. Sprinkle with almonds. Spread the compote on the dough, leaving a rim of about 4 cm all around. Fold the edge of the dough all around over the filling. Whisk the egg. Spread the rim of the dough and sprinkle with brown sugar. Bake in a hot oven on the lower shelf for 25-30 minutes. Remove the tart and let it cool down.
To make the butter easier to grate, freeze it about 30 minutes before processing.