Preheat your oven to 425°F (220°C) and position a rack in the center. This high, consistent heat is key for caramelization without steaming. On a large, rimmed baking sheet, toss the broccoli florets and stems with the neutral oil until evenly coated. Spread them out in a single layer—crowding is the enemy of crispiness. Trust me, giving each piece some space is the secret to perfect roasted broccoli.
Roast the broccoli for 15 minutes. Don't stir or shake the pan during this time. This allows the hot air to circulate and the bottoms to develop those beautiful, dark, caramelized spots. While it roasts, whisk together the sauce: soy sauce, toasted sesame oil, honey, minced garlic, grated ginger, rice vinegar, and red pepper flakes (if using) in a small bowl. The aroma will tell you this sauce is special.
After 15 minutes, carefully remove the hot pan from the oven. The broccoli should be bright green with some browned edges. Pour the sauce evenly over the broccoli. Using tongs, gently toss and turn the florets to coat them thoroughly in the glossy, fragrant sauce. Believe me, this mid-roast glazing technique infuses flavor into every nook.
Return the pan to the oven and roast for another 5-7 minutes. You're looking for the sauce to bubble and reduce slightly, and the broccoli to become tender-crisp with deeply caramelized, sticky edges. The garlic and ginger will become fragrant and mellow in the heat.
Remove the pan from the oven. Immediately transfer the broccoli to a serving platter or bowl to prevent overcooking on the hot sheet. Sprinkle generously with sesame seeds and sliced green onions. Step back and admire your work—the glossy, savory-sweet glaze clinging to crispy, vibrant green florets is a sight to behold. Serve hot and enjoy the applause.