Mix flour, 150 g sugar and salt in a mixing bowl. Add butter in pieces and milk and knead first with the dough hooks of the hand mixer, then with your hands to a smooth dough. Knead in 100 g walnuts. Then spread the dough evenly in a greased tart tin (26 cm ∅) and form a smooth base with your hands. Press the dough up at the edge. Pre-bake the base in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 15 minutes until it is slightly golden. Remove the base from the oven and let it cool down a little
Wash the plums, grate dry, halve and stone
For the filling, mix 50 g sugar, eggs, crème fraîche and vanillin sugar. Spread 50 g walnuts on the base. Spread the cream evenly on top. Arrange the plums in a circle on the cream from the outside to the inside, so that the plums overlap slightly
Continue baking the tart for about 40 minutes at the same temperature until the plums are soft and the tart is golden brown. Let the cake cool down on a cake rack, remove from the tin and sprinkle with sugar crystals
Preparation time approx. 1 hour 30 minutes