In a dutch oven, bring water to a boil. Add chicken breasts and cook till done, about 15 minutes.
While chicken breasts are cooking, go ahead and cook your egg noodles according to package directions for al dente. Drain and run under cold water to stop cooking, set aside.
Drain chicken and cut into bite sized pieces, set aside.
In the same dutch oven you cooked the chicken in, add butter, melt, then add diced onions and sliced mushrooms then cook till tender.
Add chicken and stir till chicken and onions are mixed well.
Add sour cream and cream of mushroom soup. Stir into chicken mixture.
Add cooked egg noodles and 1/2 of the bag of shredded cheddar cheese.
If mixture is too dry, you may slowly add chicken broth till it's the way you like it. At times, I have added some cream of chicken soup if I'm not going to serve it right away and stick it in the oven to keep warm.
Spoon into baking dish and top with remaining cheese. Pop into 350 degree oven till cheese is melted.
If you are going to keep it in the oven to stay warm till serving time, you may want to cover it with foil or a lid. This is great served with a salad or steamed broccoli.