For the walnut caramel tart, first preheat the oven to 175 degrees.
For the dough, quickly knead all ingredients into a smooth dough, then cover and let rest in the refrigerator for about 30 minutes.
For the nut caramel, boil 400 g sugar, lemon juice and 250 ml water, stirring constantly until the syrup caramelizes to a light brown. Remove from heat, stir in sour cream or sour cream and ¾ of the walnuts.
Cut 200 g of butter into cubes and add to the caramel. Stir until the butter has melted and combined with the caramel.
Roll out the dough on a floured work surface or baking paper to a thickness of 1 cm, place in the tart pan and press into the edges. Trim off any overhanging edge. Pour in the caramel mixture and bake in the oven for 35 minutes.
Remove the tart from the oven, let cool, then lift out of the pan. Spread the remaining walnut kernels and chill the walnut caramel tart overnight (not in the refrigerator).
Enjoy the walnut caramel tart with vanilla ice cream or whipped cream.