Preheat the oven: Preheat to 375°F (190°C). Lightly grease a 9×13-inch baking dish with butter or non-stick spray.
Layer the ingredients: Spread half of the cubed rye bread evenly in the bottom of the prepared dish. Layer with chopped corned beef, sauerkraut, and 1 1/2 cups of shredded Swiss cheese. Drizzle about 1/2 cup of Thousand Island dressing over the layers. Top with the remaining rye bread cubes.
Prepare the egg mixture: In a medium bowl, whisk together the eggs, milk, melted butter, salt, and pepper. Pour this mixture evenly over the casserole, ensuring it soaks through the bread layers.
Top and bake: Sprinkle the remaining Swiss cheese on top and add caraway seeds if desired for extra Reuben flavor. Bake uncovered for 35–40 minutes, or until the casserole is bubbly, golden, and slightly crisp on top.
Rest and serve: Let the bake rest for about 5 minutes before serving. This allows it to set and makes slicing easier. Serve warm, optionally with extra Thousand Island dressing on the side.
