Preheat oven to 350 F and grease a large casserole pan with cooking spray.
    Cut 4 slices of rye bread and cut in 2-inch cubes.
    Add last 2 slices of rye bread to a food processor and pulse until crumbled.
    Lay cubed rye bread in the casserole pan and top with half of the shredded corn beef.
    Add sauerkraut, pickles, and 1 tsp. caraway seeds evenly over the corned beef.
    Sprinkle half of the cheese over top and top with the rest of the shredded corn beef.
    Top with the remaining swiss cheese and caraway seeds.
    Combine milk, eggs, mustard, and thousand island dressing in a liquid measuring cup and whisk until combined.
    Pour over the casserole and sprinkle top with crumbled rye bread.
    Cover the casserole pan with foil and bake for 40-45 minutes.