Seafood Stew with Fennel and Thyme

Name: Seafood Stew with Fennel and Thyme
Ingredients: 1 1/2 pounds mussels, scrubbed debearded; 2 1/2 cups chopped onions; 1 cup dry white wine; 12 parsley sprigs plus 1/2 cup chopped parsley; 2 tablespoons (1/4 stick) butter; 2 cups finely chopped leeks (white and pale green parts only); 2 cups diced trimmed fennel bulb; 4 8-ounce bottles clam juice; 4 large fresh thyme sprigs; 2 bay leaves; 1 3/4 pounds thick halibut fillets, cut into 1 1/2-inch pieces; 10 ounces sea scallops; 1 cup crème fraîche*; 2 large egg yolks