Dice 200 g butter and melt in a pot. Wash lemon hot, grate dry and tear off zest. Halve the lemon and squeeze 1 half. Remove butter from the stove and let it cool down a little.
Beat the egg yolks, 2 tablespoons lemon juice and 100 ml white wine over a hot water bath until frothy. Gradually fold in the liquid butter, season to taste with the remaining lemon juice, sugar, salt and pepper.
Wash the salmon and dab dry. Bring 100 ml white wine and 1/4 litre water to the boil in a coated pan. Add the salmon, cover and cook over medium heat for 8-12 minutes. Season with salt and pepper.
In the meantime wash and drain the spinach. Peel garlic and onion and chop finely. Heat 1 teaspoon butter in a large pan. Add garlic, onion and 4 tablespoons of white wine.
Steam spinach for 2-3 minutes until it has completely collapsed. Season to taste with salt, pepper, nutmeg and sugar. Carefully reheat the sauce. Cut the remaining half lemon into slices.
Arrange salmon, spinach, lemon slices and sauce on plates, sprinkle with lemon zests.