Ingredients
Extra-virgin olive oil
1 1/2 pound boneless sirloin steak
Coarse salt
1 teaspoon ground black pepper
1 onion, cut in half and sliced
1 tablespoon unsalted butter
1/3 cup red wine vinegar
Preparation
Preheat oven to broil.
Place 12-inch cast-iron skillet under broiler for 2 minutes.
Brush olive oil onto steak. Season both sides of steak generously with salt and freshly cracked black pepper.
Add the steak to the heated pan and broil for 8 1/2 minutes.
Transfer steak to a plate to rest. Heat steak pan on the stovetop over medium heat.
Add onions and butter. Stir and cook until browned, about 6 minutes. Pour in vinegar and stir to scrape up browned bits on bottom of the pan. Let vinegar simmer until reduced, just about 1 minute.
Pour any steak juices from the resting steak into the pan. Transfer the steak to a cutting board and slice into 1/4-inch slices. Lay the steak slices on a platter and pour the sauce over top and serve.
