1. Prepare the young leeks: remove the base of the leeks and a few outer leaves if necessary. Cut them into slices and wash them. Cook them in boiling salted water for about 3 to 4 minutes, keeping them crunchy. Once cooked, drain them and set them aside. Poach the salmon trout fillet in a court-bouillon for a few minutes, then remove it and crumble it.
2. Preheat the oven to 180°C (350°F).
3. Divide the young leek slices and crumbled salmon trout fillet into small gratin dishes.
4. Gently heat the heavy cream, add the egg yolks and mix well; season with salt and pepper.
5. Immediately pour the cream into the dishes and place them in the oven; bake for about 15 minutes.