Boil 4 lobsters in water for 20 minutes, then remove them from the pot and reserve the stock.
Clean the lobsters and reserve the meat, shells, legs, and swimmerets.
Simmer lobster shells in 10 cups of the reserved stock with tomato paste for 1.5 hours, then strain.
Sauté onions, celery, carrots, thyme, parsley, and saffron with some stock, then add tomato paste and black pepper.
Combine the sautéed mixture with the strained stock in a pot and simmer.
Slowly add heavy cream and sherry, simmer for 20 minutes.
Mix cornstarch with water and add to the pot, simmer for another 20 minutes.
Serve with lobster meat and garnish with legs and swimmerets.
