Crumble the yeast and mix with sugar until the yeast becomes liquid. Put flour, 1/2 teaspoon salt, 5 tablespoons oil and 150 ml lukewarm water in a bowl. Add the mixed yeast and knead immediately to form a smooth dough. Cover the dough and let it rise in a warm place for about 30 minutes.
Wash the asparagus, cut off the woody ends. Halve the asparagus lengthways. Peel shallots and cut into strips. Mix the sour cream and crème fraîche, season with salt and pepper. Knead the yeast dough again and cut in half. Line a drip pan with parchment paper. Roll out half of the dough and use it as a base. Spread half of the sour cream on the dough. Spread the asparagus, shallots and parmesan (also half of them) evenly on top. Bake in the preheated oven (electric stove: 250 ° C / convection: 225 ° C / gas: level 5) on the lower rack for 10–12 minutes. Or of course on the grill. In the meantime, process the remaining dough and topping in the same way. Cover the finished tarte flambée with salmon and cut into pieces.