Peel, wash and halve the potatoes and cook them in boiling salted water for 6-8 minutes in a pressure cooker at level 2 until soft. Peel and clean carrots and celery and cut them first into thin slices, then thin strips.
Wash the leek and cut into thin strips. Simmer crème légère and 8 tbsp. broth in a saucepan for about 2 minutes. Wash the fish, pat dry and season with salt, pepper and a little lemon juice. Drain the potatoes, remove from the pot and keep warm.
Wash the pressure cooker and melt the fat. Briefly sauté the vegetable strips, season with salt and deglaze with 2 tablespoons of stock. Place the vegetables in the perforated steamer tray. Place fish on top, set the cooking indicator to level 1 and heat the pot with 2/3 of the stove power.
As soon as the green ring appears, the cooking time of 2 minutes begins. Wash the chervil, shake dry and chop finely, except for one leaf for garnishing. Add the chervil to the sauce and season to taste with salt, pepper and a little lemon juice.
Bind with sauce thickener. Arrange the fish on the vegetables and pour the sauce over them. Garnish with chervil. Add potatoes.