First prepare the sauce. In the time when the sauce is boiling, the fish can be prepared.
So for the sauce:
Dice the shallot very finely. Melt the butter in a saucepan and sauté the onion cubes in it. Dust with flour, let it rise briefly and then deglaze with the fish stock. Add the cream and vermouth, bring to the boil and boil the flour on a low flame for about 20 minutes.
In the meantime, heat the oil in a flat roasting pan or pan. Salt the skrei. Gently fry in the roaster on both sides over medium heat. Pour in 100 ml fish stock. Add the thyme sprigs and cook in the preheated oven at 140 ° C on the lowest rack for 6 - 8 minutes (fan-assisted approx. 6 minutes).
If you like, you can now strain the sauce through a sieve so that the onion cubes remain. Add the fish stock from cooking the skrei fillets. Then season with Szechuan pepper, thyme leaves, salt and lemon juice to taste.