Rib-Eye Steak Sandwich with Blue Cheese and Caramelized Onions and Mushrooms

grilled-rib-eye-sandwich-blue-cheese The NFL Playoffs are here! I’m rooting for two teams tomorrow. The Browns, for my friend Robert Withrow (a.k.a. Robert Christopher) and the Dolphins, for my son Max and because they’re playing the Chiefs. Double this recipe for a crowd. Rib-Eye Steak Sandwich with Blue Cheese and CaramelizedOnions and Mushrooms 1 lb. boneless rib-eye steak2 tablespoons balsamic vinegarKosher salt and fresh-ground pepper, to taste2 tablespoons olive oil1 medium sweet onion, sliced thin8 ounces cremini or white button mushrooms, sliced1 French baguette, about 16 inches long, or 4 quality rolls or buns4 ounces blue cheese4 ounces fresh spinach leaves Trim any excess fat from the steak, season with salt and pepper and drizzle each side with 1/2 tablespoon balsamic vinegar. Set aside for 20 minutes to come to room temperature.While the steak is marinating, heat the olive oil over medium heat. Add the onion and sauté, stirring frequently, until soft and translucent, 3 to 4 minutes. Add the mushrooms and continue cooking until the mushrooms are nicely browned and the onion is caramelized, 8 to 12 minutes longer. Season to taste with salt and pepper, then remove from the heat and set aside.Preheat a gas or charcoal grill to a medium-high temperature. Oil the grates, add the steak and grill to desired doneness, 2-1/2 to 3 minutes per side for medium-rare (depending on thickness). Leave the grill on. Allow the steak to rest for 5 minutes, then cut into very thin slices.To assemble the sandwiches, place the baguette or rolls on a sheet of heavy-duty aluminum foil. Line the bottom of the bread with spinach leaves, add the steak slices and top with the onion-mushroom mixture. Add the blue cheese and place the sandwich on the grill until the cheese melts, 2 to 3 minutes. Top with the other half of the baguette or rolls, press the baguette or individual sandwiches gently. Cut the baguette into 4 equal portions, or serve the individual sandwiches.