Sauté onion in butter in large saucepan until tender, but not browned, about 3 minutes. Add thyme and celery seeds; sauté 30 seconds more. Add broth, lima beans, corn and ham. Bring to boiling. Lower heat; cover and boil gently 15 minutes.
Whisk in potato flakes until liquid is thickened and smooth. Gradually stir in half-and-half and pepper. Heat to serving temperature. Makes 4 servings (about 7-1/2 cups).