Add your vegetable oil to a preheated wok. Stir your garlic, ginger, and shallots for about 1 minute.
Add in your curry paste, smashing down with a spatula. Sauté for another minute.
Add your coconut milk, coconut cream, fish stock, fish sauce, brown sugar, and juice of one lime to your wok. Stir until well mixed, then reduce heat. Allow your sauce to simmer until you see red beads of oil start to form (about 20 minutes)
Add your fish and vegetables to the wok sauce (except for mussels and shrimp), and allow to simmer until cooked. 5-8 minutes before serving, add your shrimp and mussels. Mussels are ready when shells are opened. (Discard any unopened shells)
Serve with steamed rice, and garnish with fresh basil, lime wedges, chilies, and cilantro.