Salmon Casserole

2 cups mashes potatoes
1/2 cup grated Swiss cheese
1 egg yolk
1 cup medium white sauce
15 1/2 oz. salmon

Line a greased baking dish with mashed potatoes. Add cheese and egg yolk to white sauce and pour 1/2 of it over the potatoes. Drain and de-bone the salmon. Flake fish and add over potatoes, cover with remaining sauce. Sprinkle bread crumbs over the mixture. Bake in a moderate over for 20 minutes.