In a large pot, melt butter over medium heat. Add chopped onion and minced garlic, cooking until translucent (about 5 minutes). Stir in the flour to make a roux, and cook for 2 more minutes. Gradually whisk in the chicken broth, ensuring it’s smooth, then bring to a simmer.

Reduce the heat to low, stirring in the heavy cream until well blended. Add chopped corned beef and drained sauerkraut, mixing thoroughly. Stir in the shredded Swiss cheese and Russian dressing until the cheese melts and the soup becomes creamy.

Season with salt and black pepper to taste, then simmer for 10 more minutes so the flavors combine. Serve hot, garnished with rye bread croutons and chopped parsley.