A light coconut broth bathes plump mussels, creamy potatoes and crisp-tender bok choy in this aromatic, Asian-inspired meal. Prep tip: A mussel's beard, or byssus thread, is the fiber that protrudes from the shell. Your market's fishmonger can remove them for you. Ingredient tip: Look for frozen fish stock at your natural market; it's sold in tubs, usually near the fish counter. Defrost before using.