Roll out the dough and place on a baking tray along with the baking paper. Combine the sour single cream and horseradish, spread on top of the dough. Drain the sauerkraut well, spread on top, season.
Bake for approx. 25 mins. on the bottom shelf of an oven preheated to 240°C. Remove from the oven, tear the salmon into pieces, arrange on the flatbread. Scatter the chervil leaves over the top.