Peel the shallots and cut into fine slices. Braise 2/3 of it with mustard seeds in half of the melted butter. Top up with 100 ml white wine and fish stock, but then let it boil down almost completely. Stir in the mustard, add the double cream and simmer for about 3 minutes over a mild heat. Season with salt and paprika powder. Pass through a sieve and set aside.
Salt the fish and place in an ovenproof pot or pan. Spread the remaining butter on top in flakes. Add the sprigs of dill, the rest of the wine and the remaining shallots. Close with a lid.
Cook in the preheated oven for approx. 15 minutes at 200 ° C on the 2nd rack from the bottom.
In the meantime, heat the mustard sauce again (and if you have no qualms, add whipped cream just before serving).
Carefully remove the fish from the pan and cover with sauce.
Serve with potatoes and spinach.
Note: Saving calories is of course easily possible with this recipe, but the delicious creamy taste is lost.