Put steaks out of the refrigerator to take off the chill.
Heat a medium skillet over medium heat, and add the butter. When the butter has melted add the onions and cook until caramel in color, about 20 minutes. Stir in the Worcestershire sauce and tomato paste. Reduce the heat and simmer for 5 minutes.
Put the anchos in small sauce pot with the stock and bring to a boil over medium heat. Turn off the heat and allow the anchos to steep for 5 minutes. Alternatively, put the anchos and stock in a microwave-safe bowl, covered with plastic wrap, and cook in the microwave for 2 to 3 minutes.
Heat a grill pan or grill to high.
Put the anchos and onions in a food processor. Turn the processor on and season with salt and pepper, to taste.
Season meat with salt and pepper, to taste, and drizzle with extra-virgin olive oil. Grill over high heat 5 to 6 minutes total, turning once, for rare. Remove the steak to a cutting board and let rest for 5 minutes. Thinly slice the steak and arrange on a serving platter. Serve with lots of steak sauce poured over top.