1) Toss the chicken with about half the garlic and ginger, the soy sauce, sugar, 1 teaspoon of the cornflour, 5g of the salt, the sherry, and the sesame oil in a bowl. Marinate at room temperature for 15 minutes. Mix the remaining cornflour with the 80ml or water.
2) Heat a large nonstick skillet over high heat. Add 1 tablespoons of the oil and heat. Add the broccoli stems, and stir-fry for 1 min. Add the florets and the remaining garlic, ginger, 30ml of water, and season with pinch of salt, and pepper, to taste. Stir-fry until the broccoli is bright green but still crisp, about 2 minutes. Transfer to a plate.
3) Heat the skillet again, and add 2 more tablespoons of oil. Add the chicken and stir-fry until the chicken loses its raw color and gets a little brown, 3 to 4 minutes. Return the broccoli to the pan and toss to heat through. Stir in the reserved cornflour mixture and bring to a boil to thicken. Add more water to thin the sauce, if necessary. Taste and season with salt and pepper, if you like. Mound the stir-fry on a serving platter or divide among 4 plates; serve with rice.
Cook's Note: The garlic and ginger can be chopped together in a mini chopper to save time.