Chicken al a King

I remember when Swanson used to sell this in a bag that you would boil and then pour over toast.  I like it over rice also. Now I cannot find it anywhere.  I got this recipe from my mother in law and I'm making it this week.  I'll update on whether it is good or not. 

3 Tbs butter
2 Tbs flour
1 cup chicken broth or stock
1 cup milk
2 cups chicken, diced
1 can mushrooms (use whole or you can't pick them out later)
1 small bag frozen peas

In a saucepan, melt butter. Stir in flour making a rue. Add chicken broth and milk slowly. Cook, stirring constantly so the sauce doesn't lump up. It will be like gravy. Add chicken, mushrooms (drained) and simmer.  Microwave your peas until they're just about done and then add them as well.  Serve over noodles or toast or rice.