Peel and wash the potatoes and cut into large cubes. Clean, wash and cut the cauliflower into small florets. Put potatoes in a large pot with boiling salted water and cook for about 15 minutes. Add the cauliflower about 10 minutes before the end of the cooking time. Wash salmon, cut into pieces and sprinkle with 2 tablespoons of lemon juice.
Dab salmon dry and season with salt and pepper. Heat the oil in a frying pan. Fry the salmon in it all around for about 5 minutes. Melt the fat in a pot. Sauté the flour in it. Deglaze with stock and milk while stirring. Let simmer for about 5 minutes. Season the sauce with salt, pepper, sugar and 1 tablespoon lemon juice. Drain potatoes and cauliflower and add to the sauce. Fold in the salmon carefully.
Let simmer for about 5 minutes. Season the sauce with salt, pepper, sugar and 1 tablespoon lemon juice. Drain potatoes and cauliflower and add to the sauce. Fold in the salmon carefully. Wash the dill, dab dry, chop finely and sprinkle over the cauliflower and salmon ragout. Pour the ragout into a bowl. Garnish with lemon and dill