Chicken and Broccoli Stir-fry

1 lb chicken breast (about 2 breasts), cubed
3 scallions, whites only, thinly sliced on an angle
2 cloves garlic, minced
1-inch piece peeled fresh ginger, minced
1 tblsp soy sauce
2 tblsp sugar
1 tblsp, plus 1 tsp cornstarch
1 1/4 tsp salt
1 tblsp dry sherry
1 tblsp dark sesame oil
About 1/3 c water
3 tblsp vegetable oil
5 to 6 c broccoli, trimmed sliced stalks and medium florets (keep the 2 cuts separate)
3/4 to 1 tsp red chili flakes, optional
1 tblsp hoisin sauce
toasted sesame seeds

In a medium bowl, toss the chicken with the scallion whites, about half the garlic and ginger, the soy sauce, sugar, 1 tsp of the cornstarch, 1 tsp of the salt, the sherry, and the sesame oil. Marinate at room temperature for 15 minutes. Mix the remaining cornstarch with 1/3 cup water.
Heat a large nonstick skillet over high heat. Add 1 tablespoon of the oil and heat. Add the broccoli stems, and stir-fry for 30 seconds. Add the florets and the remaining garlic, ginger, 2 tablespoons of water, and season with 1/4 teaspoon salt, and pepper. Stir-fry until the broccoli is bright green but still crisp, about 2 minutes. Transfer to a plate.
Get the skillet good and hot again, and then heat 2 more tablespoons oil. Add the chicken and chili flakes if using. Stir-fry until the chicken loses its raw color and gets a little brown, about 3 minutes.
Add the hoisin sauce, return the broccoli to the pan and toss to heat through. Stir in the reserved cornstarch 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. Garnish with sesame seeds; serve with rice.

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