Dice the onions and let half of them become translucent in the pan. Add the thawed spinach leaves and stir for 3-4 minutes. Season to taste with salt, pepper and pernod.
Roll out the puff pastry. Cut into four rectangles of 20 x 10 cm and cover half of each plate with a salmon fillet. Spread the spinach on the fish. Brush the edges with a little water and then close. Press the edge with a fork. Mix the egg yolk with a little water and brush the dumplings with it.
Bake in the preheated oven at 200 ° C for approx. 20-25 minutes.
Sweat the remaining onion cubes in butter and deglaze with white wine. Add the mustard and wormwood and let it steep for 2-3 minutes. Then add the cream and thicken slightly.