In a large casserole, bring to a boil fish fumet at medium heat. Add shrimps 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 preparation with a fine sieve. Set aside broth and seafoods separately. In the same casserole, melt butter at medium heat. Add flour an cook 1 minute while stirring.
Pour reserved broth and bring to a boil while whisking. Add cream, lobster, seafoods, salmon and sliced leeks. Season and stir. Cook 1 minutes. Divide preparation into four ramekins.
Cool down, then set ramekins in the refrigerator. Spread with Mozzarella and breadcrumbs. Set each ramekins in freezer bag. Remove air and seal.
Heat. Set on a baking sheet. Gratin in the oven for 20 to 25 minutes preheated at 205°C (400°F).
Chef’s note
This plate can be frozen 2 months. The night before, thaw in refrigerator.