ln a deep, 2 1/2-quart to 3-quart, heat-resistant, non- metallic casserole, melt butter in Microwave Oven 30 seconds. Add leeks and onions. Heat, uncovered, in Microwave Oven an additional 3 minutes.
Add diced potatoes and chicken broth to butter-leek mixture. Heat, covered, 15 to 18 minutes or until potatoes are very tender.
Press mixture through a sieve or electric blender till smooth.
Return mixture to heat-resistant, non-metallic casserole and gradually stir in cream. Add salt and pepper to taste
Heat, covered, 4 minutes or until soup is very hot.