Iberian Seafood Stew

Name: Iberian Seafood Stew
Ingredients: ½ pound Iberian salt pork; 2 tablespoons butter; 2 tablespoons flour; 1 onion; ¾ cup water or clam juice; ¼ cup amontillado sherry; 1 pound mussels; 1.5 pounds cockles or small clams; 5 prawns (shrimp); 1 quart whole milk; 1½ pounds potatoes peeled; 2 bay leaves; kosher salt; freshly ground black pepper