Let the rye bread dry out overnight or lightly toast in oven to dry the bread out.
Combine eggs, milk and mustard or caraway seeds and whisk to combine well. Set aside.
Combine in bowl the bread, corned beef, 1 cup of the swiss cheese, sauerkraut. Transfer to small buttered casserole dish. Pour the egg/milk mixture over top. Let the egg mixture soak into the bread for about 15 minutes or so. Top with remaining Swiss cheese and bake at 350° for about 30-40 minutes until set.
If desired, served with a dollop of Thousand Island dressing.