In 10-inch nonstick skillet, heat oil over medium heat. Add onion and garlic; cook 3 to 4 minutes, stirring occasionally, until onion is tender. In medium bowl, stir broth, flour, coriander and pepper with wire whisk until blended. Slowly add to hot mixture in skillet, stirring constantly. Cook and stir 5 to 6 minutes, until mixture boils and thickens slightly. Remove from heat. Stir in sour cream until well blended.