In a large soup pot or Dutch oven melt butter over medium-high heat. Add onions and mushrooms and sauté for 6-8 minutes until they become soft and golden.
Add flour and cook, stirring constantly, for an additional minute.
Add Campbell?s Mushroom Broth, dill and paprika. Reduce heat to medium-low and simmer for 10-15 minutes. Whisk in sour cream.