Divide the fish into four portions. Set them aside. We wait just before serving before preparing the fish.
When you are ready, boil 1 liter of water with 2 tablespoons of butter and a little salt in a low saucepan.
Put the fish in boiling water and remove the pan from the heat. Put a lid on and let it simmer until ready, about 5 minutes. If you are using a thermometer, the core temperature should be 40 degrees.
Coarsely chop the dill and put it in a blender. Heat the oil to 50 degrees and beat it on the dill. Blend on high speed for about 30 seconds.
Strain the oil through a fine mesh strainer and store in a glass or similar. Let the oil sit so that the water and dill residue sink to the bottom. To get completely clear oil, you can freeze it and separate the frozen water from the oil.
Peel a squash, grate it and squeeze out the juice. Store the juice in an airtight container until you need it. Leftover shredded horseradish can be frozen and used in a sauce at a later time.
Mix the cream with the vinegar until you get a suitable sour cream. Season with a little salt and add horseradish juice to desired strength.
Cool the cream slightly just before serving. Be careful not to overheat, as the strength of the horseradish decreases.
Garnish with 5 tablespoons of dill oil and serve with the fish.
Cut the potatoes, carrots and turnips into pieces of the same size.
Boil in lightly salted water until tender, but still with a small core. Serve freshly cooked.
Serve with fried mushrooms and spinach in addition to root vegetables.