Peel and wash the potatoes and cook in salted water for about 20 minutes. Clean spinach, wash thoroughly. Peel and chop the onions. Knead flour and 1 tablespoon butter, chill
Heat 2.1-2 tablespoons of butter. Sauté onions in it. Add spinach dripping wet and let it collapse. Add 1/8 l milk and cream, bring to the boil. Stir in flour butter, simmer for about 3 minutes. Season to taste with salt, pepper and nutmeg
Wash the salmon, pat dry and cut into 4 pieces. Heat the oil. Fry the salmon for about 2 minutes on each side. Season with salt and pepper. Drain the potatoes, mash them finely or press them through the potato press. Add 1/4 l milk and 1 tablespoon butter. Season with salt and horseradish
Pour the spinach into a greased casserole dish. Place salmon on top. Spray half of the puree onto the salmon stalks with the piping bag. Or spread it with a spoon. Keep the rest of the puree warm
Bake the salmon in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C / gas: level 4) for about 15 minutes until golden brown. Arrange everything