In 9 x 12 inch pan layer:

1 c. sour cream
1 lg. onion, diced
1 lg. can sauerkraut, drained
2 cans corned beef, crumbled
12-16 oz. Swiss cheese, grated

Top with 10 slices rye bread ground to crumbs. Drizzle 1/2 pound butter over top. Bake at 350 degrees for 45 minutes. (Can be made day before except for butter). Serves 8.