In a large casserole, boil fish fumet (or vegetable broth) at medium heat. Add shrimp and scallop mix, sliced leeks, and salmon cubes. Bring again to a boil, then simmer for 1 to 2 minutes at low heat.
Above a bowl, filter the preparation with a fine sieve. Set aside the broth and seafood separately. In the same casserole, melt the butter at medium heat. Add the flour and cook for 1 minute while stirring.
Pour the reserved broth and bring to a boil while whisking. Add the cream, lobster, seafood, salmon, and sliced leeks. Season and stir. Cook for 1 minute. Divide the preparation into 4 ramekins.
Cool down, then set the ramekins in the refrigerator. Spread with Mozzarella and breadcrumbs. Place each ramekin in a freezer bag. Remove the air and seal.
Heat. Set on a baking sheet. Gratin in the oven for 20 to 25 minutes preheated at 400°F (200°C).
Chef’s note
This plate can be frozen for 2 months. The night before, thaw in the refrigerator.