Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Clean, wash and drain the spinach. Peel onions and dice them roughly. Heat 30 g fat in a pot and fry the onions in it. Add the spinach and let it collapse. Dust with flour and let it sweat on.
While stirring, deglaze with cream and bring to the boil briefly. Season to taste with salt, pepper and nutmeg. Cut salmon into 4 slices. Heat the oil in a pan and fry the salmon in it for about 5 minutes on each side. Season with salt and pepper. Fill spinach into a casserole dish and place the salmon slices on top. Drain the potatoes. Add 20 g butter and mash with a potato masher. Heat the milk and gradually add it to the mashed potatoes. Season with salt. Add horseradish and stir in. Fill about half of it into a piping bag with a star-shaped spout and spray it onto the salmon slices.
Add 20 g butter and mash with a potato masher. Heat the milk and gradually add it to the mashed potatoes. Season with salt. Add horseradish and stir in. Fill about half of it into a piping bag with a star-shaped spout and spray it onto the salmon slices. Place the remaining butter as small flakes on the mashed potatoes and bake in the preheated oven (electric cooker: 225 ° C/ gas: level 4) for 15-20 minutes. Keep the rest of the mashed potatoes warm. Serve the salmon garnished with lemon slices and add the remaining mashed potatoes