In medium size saucepan over medium heat saute sliced onions in oil until wilted. Add broth; bring to full rolling boil. Remove from heat; whisk in potato flakes, evaporated milk and pepper. Cover and chill or return to saucepan and heat through. Garnish with chopped green onion. Makes 4 servings. Note: For smoother chilled soup, puree chilled base in blender or food processor; thinning it with small amounts of chicken broth or water.