Sausage in Polish Sauce

2 onions, sliced
3 tablespoons butter or 3 tablespoons margarine
1 lb smoked kielbasa
1 1/2 cups beef broth
1 1/2 cups beer
2 tablespoons flour
1 tablespoon vinegar
2 teaspoons brown sugar
3/4 teaspoon salt
1/4 teaspoon pepper
4 potatoes, peeled, boiled, and quartered
Sauté onion in 2 tablespoons butter until golden.
Add kielbasa, broth, and beer. Simmer 20 minutes.
Blend flour into remaining 1 tablespoon butter; stir into broth.
Add vinegar, brown sugar, salt and pepper.
Add potatoes. Cover and cook over medium heat 10 to 15 minutes.
Slice kielbasa into 2-inch chunks and serve.