For the dough mix 300 g flour and 1 pinch of salt in a bowl. Grate butter on a coarse grater to make flour. Wash the thyme, remove the leaves from the stalks and chop. Mix everything briefly with a wooden spoon. Stir sour cream, lemon juice and 75 ml cold water until smooth. Add to the flour mixture and knead into a smooth dough, first with a spoon, then briefly with your hands (there should still be pieces of butter in the dough). Wrap the dough in foil and refrigerate for about 1 hour.
For the topping, wash the green asparagus in the meantime and cut the ends off generously. Wash and peel the white asparagus and cut off the ends. Cut the asparagus diagonally into slices and season with 1 pinch of salt and sugar each, put aside.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Mix ricotta and eggs and season with approx. 1⁄2 tsp. salt and pepper. Roll out the dough on a piece of baking paper in a rectangular shape (approx. 22 x 42 cm). Spread with the ricotta cream, leaving a rim of approx. 2 cm all around. Whip the free edge over the ricotta cream and press down gently. Pull the tart onto a baking tray using the baking paper. Spread asparagus on top and season with pepper. Bake in a hot oven on the lowest shelf for 25-30 minutes.
In the meantime heat oil in a pan. Fry the pancetta until crispy. Take it out, let it drip off on kitchen paper and break it up roughly. Roast pine nuts briefly in hot bacon fat. Finely slice the cheese. Sprinkle tart with pancetta, pine nuts and cheese.