In a large skillet, saute onion inoil and 2 tablespoons butter until tender. Stir in broth and clam juice; bring to a boil. Add scallops, shrimp,crab and 1/8 teaspoon pepper;return to a boil.Reduce heat;simmer,uncovered,for 4-5 minutes or until shrimp turn pink and scallops are firm,stirring gently.Drain,reserving cooking liquid; set seafood mixure aside.
In a saucepan, melt the remaining butter;stir in flour until smooth.Combine milk and reserved cooking liquid;gradually add to the saucepan.Add salt and remaining pepper.Bring to a boil;cook and stir for 2 minutes or until thickened. Remove from the heat;stir in cream and 1/4 cup Parm cheese.Stir 3/4 cup white sauce into the seafood mixture.
Spread 1/2 cup white sauce in a greased 13 x 9 baking dish.Top with three noodles;spread with 1/2 of the seafood mixture and 1 1/4 cups sauce. Repeat layers. Top with remaining noodles,sauce and Parm. Bake,uncovered,at 350 for 35-40 minutes. Let stand for 15 minutes before cutting. Yield: 12 servings (?)