In a small bowl, whisk together the water (or stock), light and dark soy sauces, oyster sauce, rice wine, sesame oil, sugar, and white pepper. In a separate tiny bowl, mix the cornstarch and cold water to make your slurry.

Heat your wok or a large skillet over medium-high heat. Add the oil. Once hot, add the mushrooms and sauté without moving them for 2-3 minutes to get deeply caramelized edges. Toss and cook for another 2 minutes as they shrink and release their juices.

Toss in the minced garlic. Stir-fry for about 30 seconds, taking care not to burn the garlic.

Pour the sauce mixture into the pan. Bring it to a boil, then let it simmer for about 2 minutes so the flavors meld and the mushrooms soak up the liquid.

Stir your cornstarch slurry one more time (it tends to settle at the bottom) and pour it into the boiling pan. Stir continuously for 30-60 seconds until the sauce turns glossy and thickens to coat the back of a spoon.

Turn off the heat and garnish with chopped spring onions if desired.