Chicken & Rice Soup

This is my aunt's recipe, but super yummy!

6 T butter
1 T onion
1/2 C flour
2 1/2 C chicken broth (1 can + 1/2 C water works fine)
1 pkg Rice-A-Roni long grain & wild rice, cooked according to pkg
2 C chicken, cubed & cooked
1/2 C grated carrot
12 oz. evaporated milk

Melt butter & saute onion. Add flour & whisk, then gradually add broth. Boil about 1 min. You will see it change quickly. Stir in carrot, cooked rice & cooked chicken. Simmer 5 min or until carrot is tender. Add evaporated milk & heat. Serve with grated Chedder cheese.