Broccoli and Beef With Oyster Sauce

In a medium bowl, stir 1 Tbsp. each soy sauce and sherry, 2 tsp. cornstarch, 1 tsp. sugar and a generous grind of pepper until sugar has dissolved. Stir in beef. Let stand for 15 minutes.In a small bowl, whisk remaining 2 tsp. each soy sauce and sherry, 1 tsp. each cornstarch and sugar, broth, oyster sauce and sesame oil.In a 12-inch nonstick skillet, heat 1 1/2 tsp. peanut oil over medium-high heat until very hot; swirl to coat skillet. Spread half of beef in a single layer. Cook, undisturbed, for 90 seconds to sear, then stir-fry for 30 seconds. Transfer to a plate. Add another 1 1/2 tsp. peanut oil; repeat with remaining beef.Add 2 tsp. peanut oil and broccoli to skillet; stir-fry for 1 minute. Make a well in center and add remaining 1 tsp. peanut oil, scallion, garlic, ginger and red pepper flakes. Stir-fry until just fragrant, about 30 seconds. Add 1/3 cup water and cover skillet; steam until broccoli is just crisp-tender, about 3 minutes.Return beef to skillet. Whisk sauce and add to skillet. Cook, tossing well, until sauce is bubbling and thickened, about 1 minute. Serve with jasmine rice, if desired.