For the béchamel sauce, heat 60 g butter. Lightly sauté the flour in it. 1⁄2 Add l water and milk while stirring, bring to the boil and stir in the stock. Simmer for about 5 minutes. Season to taste with lemon juice, salt and pepper.
Clean, quarter, wash and cut the savoy cabbage into strips. Wash and slice the tomatoes. Wash salmon, dab dry and cut into cubes. Grease an angular casserole dish.
Put 3 tablespoons of béchamel sauce into the mould and spread. Place 3-4 lasagne plates on top. Spread with a layer of sauce. Spread about 1⁄3 of the tomatoes, half savoy cabbage and half salmon one after the other.
Layer the remaining ingredients, finishing with tomatoes. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) for 30-40 minutes.