This soup is amazing and really versatile! It ends up making it's way into my meal list just about every week it's so good. I make a few changes, though, to solve the cheese clumping problem and lower the fat. I use low fat plain yogurt in place of the sour cream and a low fat mix of shredded gouda/mozzerella at the end. (I've never had a lot of luck with low fat cheddar...) I also reduce the amount of cheese called for in the recipe by between 50% and 75%. I haven't ever had a problem with the cheese clumping or sticking since I made these modifications. I've also made the soup without celery and without sour cream/yogurt. While it's very, very best with the yogurt, it also tastes great without this ingredient if you don't have it on hand.