In a large pot over medium heat, melt 4 tablespoons of unsalted butter until bubbly. Add 1 finely chopped onion and 2 minced garlic cloves, cooking for about 5 minutes until the onion becomes translucent and fragrant.

Sprinkle in 1/4 cup of all-purpose flour and stir continuously for 2 minutes to form a roux.

Gradually whisk in 4 cups of chicken broth, ensuring to dissolve any lumps from the roux. Increase the heat slightly until the soup begins to simmer, then reduce to low heat and cook for about 5 minutes.

Lower the heat further and stir in 1 cup of heavy cream, mixing thoroughly until the soup is well combined and creamy.

Fold in 2 cups of chopped corned beef and 1 cup of well-drained sauerkraut, stirring until evenly distributed. Let it simmer for another 5 minutes over low heat.

Sprinkle in 1 cup of shredded Swiss cheese along with 1/2 cup of Russian or Thousand Island dressing, stirring continuously until the cheese fully melts.

Taste your soup and season it with salt and pepper as needed, adjusting based on your preference.

Allow the soup to simmer gently on low heat for an additional 10 minutes. Serve garnished with rye bread croutons and chopped parsley.