Recipe is really short, so here's pretty much the full thing:

Sauerkraut Soup Russian-Style

3 to 4 tablespoons butter (am substituting with margarine)
1 onion, sliced
2 small carrots, sliced
1 potato, peeled, sliced
2 tablespoons flour
1 teaspoon tomato puree
1/4 pound sauerkraut
4 to 5 cups Basic Beef Stock (references other recipe in book, substituting with premade vegetable broth)
1 tablespoon chopped parsley (substituting with half the amount in dried parsley)
1 teaspoon chopped chervil (might omit or replace with half amount herbes de provence since store doesn't sell)
Sour cream

Melt butter; cook onion and carrots until golden. Add potato. Stir in flour; when smooth, add tomato puree and sauerkraut. Cook a few minutes; stir constantly. Add stock and herbs; bring to boil. Simmer about 40 minutes; season to taste. Serve hot with sour cream in each soup cup. Yield 4 to 6 servings.