Sauté chopped onion in 1 tablespoon oil in soup pot.
Add 43.5 ounces chicken broth and bring to boil.
Add 32 ounces bag frozen diced hash browns and bring to boil.
Add 10.5 ounces condensed cream of celery soup, 10.5 ounces condensed cream of chicken soup, and 12 ounces evaporated milk, bring to a simmer.
Using an immersion blender, blend the soup until it is thickened with a few potato chunks remaining (about 2-3 minutes). Remove blender. (If you do not have an immersion blender, you can mash the tender potatoes in the pot with a serving spoon.)
Add 14 ounces shredded cheddar cheese.
Heat, stirring frequently, until cheese melts.
Season with salt & pepper to taste
Serve garnished with 2 ounces shredded cheddar cheese and chopped green onions.
Notes
If you have sautéed onions in the freezer, use the equivalent of 1 onion. If not, consider sautéing a whole bag of onions either while preparing this dish or later when you have more time and freezing them in 1 cup portions. Next time a recipe calls for a sautéed onion, you have it already prepared!
For a vegetarian version of this soup, use vegetable stock in place of chicken broth, and use two cans of cream of celery soup and omit the cream of chicken soup.