For the dough, knead 500 g flour, 350 g sour cream and butter in flakes first with the dough hooks of the mixer, then with your hands to a smooth dough. Cover and chill for about 45 minutes.
For the filling, roast pine nuts in a pan without fat until golden brown, remove and let cool. Mix 350 g sour cream and horseradish. Season to taste with salt. Cut salmon into strips. Wash the dill, shake dry and chop coarsely.
Roll out the dough on some flour to a thickness of approx. 1⁄2 cm. Cut out 14 circles (each approx. 15 cm Ø), knead the rest again and again, roll out and cut out. Spread approx. 1 tbsp. sour cream on each circle, leaving a rim of approx. 3 cm all around.
Spread salmon, pine nuts, drained capers and dill on the sour cream. Press the edges of the dough firmly together over the filling.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Line two baking trays with baking paper. Place the dumplings on top with some space between them. Whisk the egg yolk and approx. 2 tsp. water.
Coat the pockets thinly with it. Bake one after the other in a hot oven for about 30 minutes. Remove, warm or cold