Preheat the oven to 350 degrees. Place the onion wedges in the baking dish. Drizzle with the oil and sprinkle with just a little salt. Stir to coat all the pieces evenly. Roast onions, uncovered, until browned and soft, about 1 hour. Remove and let stand until slightly cooled.
Put the onions in the blender. Add the broth and soy sauce and blend to a smooth puree. Transfer the sauce to a small saucepan or a microwavable dish, cover and set aside.
Preheat the broiler or prepare coals for grilling.
Press the cracked pepper onto both sides of each steak, using about 1 teaspoon of pepper for each steak. Broil or grill the steaks until seared and nicely browned on one side, about 4 minutes for medium-rare and 5 minutes for medium. Turn and cook 4 minutes more for both medium-rare and medium.
Reheat the onion sauce on the stovetop or in a microwave oven while the steaks are cooking. Spoon the warmed sauce over each steak and serve.
