MELT butter in large saucepan or Dutch oven on medium heat. Add onions and celery; cook and stir 5 min. or until crisp-tender. Add next 4 ingredients; bring just to boil, stirring constantly. Slightly crush potatoes with back of spoon. Simmer on medium-low heat 5 min., stirring frequently.
RESERVE 2 Tbsp. each bacon and cheese and 1 Tbsp. green onions; set aside. Add remaining bacon, cheese and green onions to soup; cook until cheese is melted, stirring constantly.
SERVE topped with reserved bacon, cheese, green onions and sour cream.