Hamburger steak smothered in brown gravy with mushrooms and onions

2 lbs Ground Chuck

1 Yellow Onion thinly sliced

16 oz mushrooms I used a blend of cremini and shitaki

2 cups beef broth – divided. I use canned fat-free low sodium

2 tbsp all-purpose flour

6 tbsp butter

4 sliced scallions white and green sections

salt and pepper to taste