Whisk all the sauce ingredients together. Give it a little taste. If you like things a little spicier, by all means, add more pepper. I even added a bit of Korean red pepper (Gochugaru), but I'm crazy like that. If you want the sauce a little milder, or without heat, you should've thought of that before, silly! You're either reading this recipe in full before proceeding, like you should, or you need to go back in time and add less/no red pepper. Divide the sauce into two containers, and add 1 tbs of cornstarch to one half. Set this aside for later.

Place your beef in the freezer for 20-30 minutes to partially freeze. It will make slicing it much easier. Slice against the grain, like in the picture (not along the little strands you see in the meat, but slicing across them. This makes the meat more tender because it shortens the muscle fibers... science). Put the meat into a zip-top bag, add your container of sauce (the half without cornstarch), and marinate the meat for 30 minutes to one hour in the refrigerator.

Slice all of your vegetables. You'll be cooking the bok choy separately, but the onions, peppers, and chilis can all hang out together.

Remove the beef strips from the marinade and dry off by laying on a piece of paper towel and patting the top with another piece.  Place ½ cup of cornstarch in a plastic zip-top bag. Place the beef strips in the bag and shake it in the cornstarch, coating lightly. Shake off the excess cornstarch, and place them on a baking sheet. Heat your oil in a wok or large frying pan over high heat.

Fry the beef on the first side for 1-2 minutes or until light golden brown. Flip over and fry the other side.  Set the cooked beef aside on a rack over a sheet pan. (Let's keep it crispy folks!)

Clean out the wok/pan.  Stir-fry the bok choy in a small amount of oil (1-2 turns of the pan) over high heat until crispy/tender and slightly charred.  Set aside and repeat with all rest of the vegetables. As you can see, I cooked the beef and bok choy in my cast iron pan and the vegetables in my wok. That's because I grossly underestimated the amount of food I would have to fit in my pan when all was said and done. Don't be like me. Plan accordingly. Use a big enough pan the first time 😉.

Return all the vegetables and the beef to the pan.  Give your reserved container of sauce with cornstarch a quick whisk, and pour over everything. Quickly toss everything together until it's all coated in the sauce. It will thicken and cover everything in sticky, yummy goodness.  Sprinkle with a bit of sesame seeds and serve over rice. Or not! I didn't need rice. It was pretty gosh darn good all by itself. Share with others. Or not! It's also pretty gosh darn good enough to be selfish and take it all for yourself and feel okay about it. Your choice.