Marinated Steak Bites with Caramelized Onions and Mushrooms

For the Marinated Steak Bites: Combine the balsamic vinegar, soy sauce, olive oil, dried mustard, and red pepper flakes in a bowl. Add the steak and mix everything thoroughly. Marinade for at least 3 hours or more in the refrigerator.

For the Caramelized Onions and Mushrooms: Chop the onion and mushrooms. In a separate pan, melt the butter over medium heat. Add the chopped onions and mushrooms, season with salt and pepper, and cook until they are caramelized, stirring occasionally. Add the Worcestershire sauce towards the end and stir.

To Cook the Steak: Heat a pan over medium-high heat. Cook the marinated steak in batches, searing both sides for about 2 minutes per side until browned. Remove the cooked steak and set aside. Add the remaining marinade sauce back into the pan along with the cooked caramelized mushrooms and onions. Heat through until the sauce simmers and thickens slightly. Return the cooked steak bites to the pan and toss to coat. Serve immediately with your favorite sides like mashed potatoes and asparagus.