Preheat the oven to 425°F. Line two rimmed baking sheets with parchment paper.
Spread the broccolini on the baking sheets, dividing them evenly between the two pans.
Drizzle the broccolini with the olive oil, using 3 tablespoons for each pan. Use your hands to coat it in the oil, paying special attention to the florets.
Sprinkle the broccolini with kosher salt, black pepper, and garlic powder.
Place the pans in the preheated oven. For even roasting, I place one on the top rack and one on the bottom rack.
Roast the broccolini until the stalks are tender-crisp and the florets begin to brown, for about 15 minutes. If you want it browned with crispy florets, roast it for 20-25 minutes. Serve immediately.
Video
Notes
Using bagged pre-washed broccolini helps with browning because it ensures it is completely dry when you coat it in olive oil.
You can adjust the baking time according to your preferences. If you'd like the broccolini tender-crisp, green, and browned just in spots, roast it for about 15 minutes. If you prefer it browned and crispy, roast it for 20-25 minutes.
The secret to this recipe is to use plenty of good olive oil and kosher salt. However, if you use any salt other than Diamond Crystal - even a different brand of kosher salt - use just one teaspoon.
You can use less olive oil, but it won't be as good. You can use just ¼ cup of olive oil, or use olive oil spray. Whatever you do, ensure the broccolini is well coated in oil. Otherwise, it could burn.
There's no need to flip the broccolini midway. You can swap the pans' locations and rotate them 180 degrees. While not mandatory, it promotes even roasting.
I don't recommend using frozen broccolini in this recipe.
You can keep the leftovers in the fridge, in an airtight container, for up to four days. Reheat them in the microwave or in a 350°F oven. They lose their crispness but not their deliciousness! You can also enjoy the leftovers cold, antipasti-style.