Preheat oven to 350 degrees.

Cut the onions about 1 inch from where the red part stops. Reserve tops for garnish.

Cut off root bottom of onions and then cut in half lengthwise. Place onions in a baking dish. Pour olive oil and balsamic vinegar over the top. Sprinkle with salt. Gently toss. They may start to separate, that is fine.

Place onions in preheated oven and cook for 15 minutes. Remove from oven.

Heat a cast iron skillet over medium high heat.

Liberally season both sides of the steak with salt and pepper.

Place steaks in skillet and sear for 30 seconds - 1 minute on each side. The steak with come away from the pan easily when ready.

After turning the steaks, place roasted onions around and on top of them.

Transfer steaks, in skillet, to preheated oven and cook for 5 minutes for medium rare. Remove from oven and let rest for 10 minutes. Garnish with a few pieces of chopped tops. Serve.