Cook the Noodles:

Boil lasagna noodles in salted water until al dente. Drain and set aside.

Make the White Sauce:

Melt butter in a saucepan over medium heat. Stir in flour and cook for 1 minute. Gradually whisk in milk, cooking until thickened. Remove from heat and stir in ½ cup shredded Swiss cheese.

Prepare the Dressing Mix:

In a small bowl, combine Thousand Island dressing and sour cream.

Layer the Bake:

Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.

Spread a thin layer of the white sauce on the bottom. Add a layer of noodles or rye bread slices.

Spread with the dressing mix, then layer corned beef, sauerkraut, and Swiss cheese. Repeat layers, ending with noodles or bread. Top with remaining white sauce and Swiss cheese.

Bake:

Cover with foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until golden and bubbly.

Serve:

Let the bake cool slightly, then slice and garnish with fresh parsley.