Begin by slicing the beef thinly against the grain, which helps shorten the muscle fibers and ensures the meat stays tender during quick cooking. Lay the slices out on a plate or cutting board and set them aside while you prepare the rest of the ingredients. Taking this step first makes the cooking process smoother and more efficient once the pan is hot.

Heat a large skillet over medium-high heat and add a small amount of oil, allowing it to heat until shimmering. Carefully place the beef slices into the pan in a single layer, making sure not to overcrowd the skillet. Let the beef sear undisturbed for a short moment to develop color, then gently flip and stir until the pieces are browned on all sides. Once browned, remove the beef from the skillet and set it aside to prevent overcooking.

Using the same skillet, add the sliced mushrooms. Spread them out evenly and let them cook without stirring too much at first so they can release their moisture and begin to brown. Stir occasionally as they soften and turn lightly golden, allowing them to absorb the savory flavors left in the pan from the beef.

Add the broccoli florets to the skillet with the mushrooms and stir to coat them in the remaining oil and pan juices. Cook until the broccoli turns a bright, vibrant green and becomes crisp-tender. It should be cooked through but still slightly firm, adding a pleasant texture to the dish rather than becoming soft.

Return the cooked beef to the skillet, along with any juices that may have collected on the plate. Pour in the prepared sauce ingredients and gently stir everything together so the beef and vegetables are evenly coated. Lower the heat slightly to prevent the sauce from reducing too quickly or burning.

Let the mixture simmer briefly, stirring gently, until the sauce thickens and clings to the beef, broccoli, and mushrooms. Once everything is evenly coated and heated through, remove the skillet from the heat and serve immediately while the dish is hot and glossy for the best flavor and texture.