Defrost puff pastry sheets against each other.
Drizzle salmon side with juice of one lemon. Clean broccoli, rinse and cut into smaller pieces. Then blanch in bubbling boiling salted water for about 3 minutes and rinse with ice cold water. Chop half of the broccoli very finely, grind the rest.
Peel shallots, chop finely and sauté in half of the butter, add broccoli, sauté briefly, remove from heat. Mix with breadcrumbs, egg and half of the yolks, season with horseradish (if desired), a little grated lemon zest and juice of one lemon, salt and pepper.
Preheat electric stove to 225 degrees. Rinse a baking sheet with cold water.
Place puff pastry sheets on top of each other and roll out to twice the size of the salmon. Lightly season the salmon all over with salt, season with pepper, rub with horseradish only very thinly to taste. Spread just under half of the broccoli in a strip the width of the salmon on the puff pastry, place salmon on top and spread with the remaining broccoli farce. Wrap salmon completely in puff pastry. Brush edges with water and press down well. Cut pastry scraps into small pieces, decorate salmon with them. Brush with beaten egg yolk.
Bake in the oven for 30 to 35 minutes (gas: level 4).
Rinse, clean and sort out the spinach leaves. Briefly in bubbling boiling salted water form, remove, ice cold quench. Steam briefly in the remaining butter until soft, mix with