HEAT oil in large stockpot on medium-high heat. Add onions, curry powder and cinnamon; mix well. Cook 3 to 5 minutes or until onions are tender, stirring occasionally.
ADD sweet potatoes, chicken broth, sour cream, milk and brown sugar; stir with wire whisk until well blended. Cook until thoroughly heated, stirring occasionally. (Do not boil.)
STIR in steak sauce. Season wtih salt and pepper to taste.