In a large bowl, combine the salmon, onion, bread crumbs and butter. Stir in the egg yolks, lemon juice, parsley, salt and pepper. , In a small bowl, beat the egg whites on high speed until stiff peaks form. Fold into salmon mixture. , Transfer to a greased 8x4-in. loaf pan. Place in a larger baking pan. Add 1 in. of hot water to larger pan. Bake at 350° until a knife inserted in the center comes out clean, 40-45 minutes. Let stand for 10 minutes before slicing., Meanwhile, in a small saucepan, melt the butter. Stir in flour until smooth; gradually add milk. Bring to a boil; cook and stir until thickened, 1-2 minutes. Stir in olives. Serve with salmon loaf.