Bring enough water to a boil to cover lobster tails; add 1 tsp salt to each 1 litre of water. Drop frozen lobster tails into water and boil 11 minutes (or 3 minutes plus the weight of the largest lobster tail) Remove meat from lobster shells and dice. Set aside. Crush shells and put in saucepan. Add the 3 cups water, seasoned stock base, onion flakes, coriander seed, bay leaf, vegetable flakes and peppercorns. Simmer 30 minutes; strain. Melt butter; stir in flour, bon appetit and salt. Cook until bubbly. Remove from heat and add milk. Simmer over low heat, stirring constantly, until thickened. Stir in lobster stock, lobster meat and cream. Do not allow it to boil. Serve piping hot.