Make a slurry of water and cornstarch to ensure it’s completely dissolved, then add to the sauce. Set aside.
Dice the steak into large one-and-a-half-inch cubes. You want the pieces to be big enough that you can sear and caramelize the steak, but keep it medium rare in the centre.
Tenderizing the steak is optional, but highly recommended for the tender texture. Dissolve baking soda into water, add cubes, let them sit for 15 minutes, then discard liquid. Rinse steak, then dry on a paper towel.
Heat a wok or stainless frying pan over high heat. Season steak liberally with salt and pepper.
Add grapeseed oil and sear the cubes until they’re cooked to approximately 85 percent of the desired doneness, about two to three minutes. Remove the steak to a plate and reserve.
Return the same pan to the stove. Lower heat to medium-high, and add butter and sliced mushrooms. Sauté for two minutes. Add onions, garlic, and ginger and cook for about a minute.
Deglaze with Shaoxing wine. Scrape all found at the bottom of the pan. Add sauce and allow to come to a boil to fully thicken.
Return the steak cubes to the sauce, cook to desired doneness, and plate in the centre of a large plate.
Return the pan to the heat, add the spinach, wilt gently and arrange around the steak.
Garnish with crispy shallots. Serve with steamed white rice. Enjoy!