Fillet the salmon using a flexible knife, carefully following the central bone. Remove the skin and bones.
Heat the peanut oil in a saucepan over high heat. Add 1 chopped carrot, 1 chopped onion, the crushed fish head and bones, and the bouquet garni. Cook over medium heat for 20 minutes. Strain the mixture; you should have about three glasses of stock. Reserve.
Cut the salmon flesh into even slices, reserving scraps to yield 100 g net along with the white fish meat. Process in a food processor for 2 minutes. Add the cream and egg, then season with salt and pepper. Blend again until you achieve a smooth, fine mousse.
Peel and finely dice the remaining carrot and onion. Blanch in boiling salted water for 3 minutes, then refresh under cold water. Fold into the mousse along with the roasted crushed peanuts and chopped chives.
Season the salmon slices with salt and pepper. Place a tablespoon of mousse on each slice, roll into paupiettes, and secure with olive picks.
Arrange the paupiettes in a baking dish with the reserved stock and chopped shallots. Bake in a preheated oven at 190°C for 10 minutes, turning halfway. Keep the paupiettes warm.
Strain the cooking liquid into a skillet and reduce over high heat. Whisk in the butter to create a glossy red butter sauce. Adjust seasoning to taste.
Plate by spooning a small ladle of sauce in the center of each dish, topping with the paupiettes, and garnishing with chervil sprigs.
This sophisticated dish requires time and care, but much can be prepped ahead. Ideal for special occasions, pair with a full-bodied red wine for an exquisite meal.
