Flank Steak with Shiitake Mushroom Sauce

Why I Love This Recipe
My version of the original recipe, which is from Cooking Light
Ingredients You'll Need
Steak:
teaspoon salt
teaspoon black pepper
(1-pound) flank steak, trimmed
Olive oil
Sauce:
1 tbsp butter
1/2 cup chopped onion
garlic cloves, minced
1/2 pound mushrooms, sliced (I like crimini)
sprig of fresh thyme, or pinch of dry
cup beef broth
cup sherry
tablespoon balsamic vinegar
salt and pepper
(original recipe calls for green onions to be added in at the last minute but I don't like green onions
Directions
Preheat broiler.
To prepare steak, rub with olive oil and sprinkle salt and pepper evenly over both sides of steak. Place steak on a broiler pan; broil 5 minutes on each side or until desired degree of doneness. Remove the steak from oven; loosely cover with foil.
To prepare sauce, heat a large nonstick skillet over medium-high heat. Melt butter in skillet. Add onion and a little salt; sauté 2 minutes.
Add mushrooms, garlic and thyme; sauté for 4 minutes. Add a little more salt to draw out juices.
Add broth, sherry, and vinegar. Bring to a boil and cook until reduced to 3/4 cup (about 8 minutes). Season to taste with salt and pepper.
Slice steak diagonally across the grain into 1/4-inch slices. Serve steak with mushroom sauce