In a mixing bowl, add the sliced beef, soy sauce, dry sherry (or apple cider vinegar), beef broth, sesame oil, sugar, ground black pepper, and cornstarch. Let it sit for 10 minutes or marinate for up to 24 hours.
Add oil to a wok or non-stick pan and place it over medium heat. Once hot, add the beef (reserve the remaining sauce) and sear on all sides. Remove from the pan.
Clean the pan, add more oil, then add the bell peppers and onions. Saute for 3-4 minutes, before removing them off the heat and adding them to the beef.
Return the wok to the heat and let it start to smoke. Once smoking, add the seared steak, vegetables, garlic, and ginger. Cook for several minutes, then toss through the leftover sauce from the beef. Cook everything together for 1-2 more minutes.
Remove the stir-fry off the heat and serve immediately.
Notes
TO STORE: Store leftovers in an airtight container in the refrigerator for up to 3-4 days. TO FREEZE: Let the beef cool completely, then transfer to a freezer-safe container and freeze for up to six months.TO REHEAT: Microwave leftovers in 30-second intervals until warm or in a skillet over medium heat.