Pour the broth into a large soup pot. Add carrots and celery and bring to a boil. Turn down and simmer till veggies are tender.

In another pan, melt the butter and cook onion over medium heat.

Whisk in flour and cook for a minute or two. Add milk, cooking till smooth and thickened.

Add milk mixture to broth.

Stir in cheese and cook till melted.

Season with salt and pepper.