Steak Tips with Mushroom-Onion Gravy

This was a delish dinner and pretty quick to put together.  Jeff, of course, would prefer that I leave the onions out, but Amelia and I really enjoyed them.  I used about 1/2 of a medium sized onion.  I'm not sure why you have to heat the whole pan in a 500° oven rather than just searing the meat on high heat but we did it anyway.  We just used a London broil that I had in the freezer and I forgot to add the red wine vinegar at the end, so go ahead and add that in if you feel so inclined.  ;)  We served this with mashed potatoes.  Deeeelish!

Steak Tips with Mushroom-Onion Gravy

2 pounds sirloin steak tips, trimmed and cut into 1 1/2-inch pieces
salt and pepper
1/4 C vegetable oil
1 pound mushrooms, trimmed, sliced 1/4 inch thick (white or baby portobello)
1 medium onion, halved and sliced thin
2 garlic cloves, minced
2 tsp tomato paste
1/4 tsp minced fresh thyme  or 1/4 tsp. dried
3 Tbsp all-purpose flour
1 can beef broth
1 Tbsp Worcestershire sauce
1 Tbsp. chopped fresh parsley (optional)
2 tsp red wine vinegar

Adjust oven rack to middle position, place 12-inch cast-iron skillet on rack, and heat oven to 500°.  Meanwhile, pat steak tips dry with paper towels and season with salt and pepper.
When oven reaches 500°, carefully remove skillet from oven using potholders and place over medium heat; turn off oven.  Being careful of hot skillet handle, add 2 tablespoons oil and heat until just smoking.  Brown half of the steak tips on all sides, 6 to 8 minutes; transfer to bowl.  Repeat with 1 tablespoon oil and remaining steak tips; transfer to bowl.
Add remaining 1 tablespoon oil to fat left in skillet and heat over medium heat until shimmering.  Add mushrooms, onion, and 1/4 teaspoon salt, and cook, stirring occasionally until mushrooms have released all their liquid, about 5 minutes.  Continue to cook until vegetables begin to brown, 4 to 6 minutes.
Stir in garlic, tomato paste, thyme and cook until fragrant, about 30 seconds.  Stir in flour and cook for 1 minute.  Stir in broth and Worcestershire sauce, scraping up any browned bits and smoothing out any lumps.
Bring gravy to simmer, then stir in browned beef and any accumulated juices.  Recuce heat to medium-low and simmer, stirring occasionally, until beef is cooked to your preference. 
Remove from heat and stir in parsley and vinegar and season with salt and pepper to taste.
Serve alone or with mashed potatoes.

Recipe altered slightly from America's Test Kitchen