In a heavy kettle, spray with cooking spray and tender apples are chopped, add onion, celery, until low heat often. Add cubed and cook until apples are cooked. Reduce heat to a boil. Cover and simmer 15 to 20 minutes) or set aside. Strain liquid thoroughly. Puree the apple-squash mixture, then combine with remaining liquid and one cup sour cream to reach desired consistency. Garnish with grated apple, sage.