Steps

• Begin by preparing your beef. Slice it into thin strips for even cooking.
• Heat a large skillet over medium-high heat and add a bit of oil. Once hot, add the beef strips in batches, searing them until they're browned on the outside but still pink in the center.
• Remove the beef and set it aside. In the same skillet, add onions and cook until translucent, then add mushrooms. Cook until they release their juices and turn golden brown.
• For the sauce, combine sour cream, beef broth, and a touch of mustard in the skillet. Whisk together until smooth.
• Return the seared beef to the skillet and let it cook in the sauce for a few minutes until heated through.