Keto Beef with Broccoli

Freeze steak for 15 minutes, then very thinly slice against the grain and season with salt and pepper.  In a large non-stick skillet over high heat, heat oil. Sear steak until seared and golden, about 3 minutes. Transfer to a plate. Reduce heat to medium and add soy sauce, garlic, ginger, and apple cider vinegar. Add broccoli and let simmer until broccoli is cooked though and sauce is reduced by half, about 5 minutes. Return beef to pan, along with any juices, and heat until just cooked through, about 1 minute.  Drizzle with sesame oil before serving.