I made this for the first time in Maine. My daughter, Terri had a huge party on Labor Day one year and I thought this would be great for a start to the menu! EVERYONE loved it; especially one very close friend, Norma! This is her recipe now and forever, I think! It was that good!
In a large pot saute onions in butter until tender. Add flour, salt, pepper to make a smooth paste combining with the sauteed onion. Stir until smooth. Gradually add water stirring constantly and bring to boil. Cook and stir for 1 minute after boiling.
Add mushrooms, celery, potatoes, carrots and reduce heat to simmer for 30 minutes until veggies are tender. Add half and half cream along with the parmesan cheese. Heat through making sure parmesan cheese melts. Remove pot from heat!
At the party, I put the soup into a crockpot on low to keep it hot. It worked just great and everyone was happy.