Preheat oven to 425 F.
Coat chicken with flour.
Pour melted butter in baking dish. Add chicken in a single layer. Bake, uncovered, for 30 minutes. Turn chicken and then bake until brown (about 20 minutes).
Remove from oven and reduce heat to 325 F. Discard extra fat.
Combine milk, soup, cheese, salt and pepper.
Add onions and mushrooms to chicken.
Pour mixture over chicken.
Sprinkle with paprika.
Cover dish with foil.
Return to oven and bake for 15-20 minutes longer.