Do you make cream soups? It is fairly easy. After frying the onion and celery, add 1\4 cup of flour and let it cook for a minute or so and then add the cooking liquid in the recipe. The soup will thicken and if you want, add a half a cup of cream, milk or half and half at the end.
I'm not really into cream soups. Mushroom, potato and broccoli are ok sometimes but I don't make them very often. I prefer broth because it's not so rich.