Recipes Ingredients Meat & Poultry Beef Recipes Steak Sandwiches with Sauteed Mushrooms and Spinach 2.8 (19) 1 Review By Martha Stewart Test Kitchen Martha Stewart Test Kitchen The recipes developed by our test kitchen team have undergone a rigorous process of development and testing, ensuring that every element is optimal, from ingredient amounts to method and cooking time. This process includes triple-testing recipes to ensure they meet our high standards. The many stellar cooks and food editors who have been part of our team include Sarah Carey, Lucinda Scala Quinn, Jennifer Aaronson, Shira Bocar, Anna Kovel, Greg Lofts, Riley Wofford, Lauren Tyrell, and Lindsay Leopold. Editorial Guidelines Updated on June 12, 2017 Print Rate It Share Share Tweet Pin Email Prep Time: 30 mins Total Time: 30 mins Servings: 4 With just a skillet, you can turn a classic steak dinner into a handheld affair. Ingredients 1 teaspoon vegetable oil 2 New York strip (shell) steaks (8 ounces each) Coarse salt and ground pepper 1 medium yellow onion, thinly sliced 8 ounces white button mushrooms, thinly sliced 1 tablespoon red-wine vinegar 1 bag (10 ounces) baby spinach 4 teaspoons grainy or Dijon mustard 8 slices crusty bread, toasted Directions In a large skillet, heat oil over medium-high. Season both sides of steaks with salt and pepper. Cook steaks until medium-rare, about 5 minutes per side, flipping once. Transfer to a plate; tent loosely with foil to keep warm. Add onion to pan; season with salt and pepper. Cook until onion begins to soften, about 4 minutes. Add mushrooms; season with salt and pepper. Cook until mushrooms brown, about 6 minutes. Add vinegar and any accumulated juices from steaks; cook until evaporated, about 30 seconds. Transfer mushroom mixture to a medium bowl. Add spinach to pan; season with salt and pepper. Cook, stirring, until wilted, about 3 minutes. Thinly slice steaks against the grain. Spread mustard on 4 slices bread. Dividing evenly, top with sliced steak, mushroom mixture, and spinach. Top with remaining bread. Serve immediately. Cook's Notes You can substitute flank or skirt steak, but make sure to slice it very thinly against the grain. Rate it Print