Cook noodles in 2-3 cups of chicken broth + enough water to be enough liquid
Stir 2 Tbsp of flour in sour cream
Take chicken out of onions
Add sour cream mixture to onions
Heat but don't boil
stir half onion mixture in noodles
Place noodles in casserole, chicken on top, rest of sour cream mixture on chicken, cover, and heat through 1/2 hour at 325 F (if refrigerated, 1h15m at 300 F)