Cooking beef for pepper steak
Meat in stir-fries is often velveted. That makes for a supremely soft chunk of meat, and it can be done with any type of meat. This answer actually addresses chicken: How to cook extremely soft chicken?, but it applies just as well to beef. It's usually done with egg and cornstarch, but sometimes it's done with a small amount baking soda instead, as in this recipe for Beef and Broccoli.