Preheat oven to 425°. Trim leaves from broccolini if you like (for a tidier look). Arrange broccolini in a single layer on 2 large rimmed baking sheets.
Drizzle oil over broccolini, sprinkle with salt and pepper, and turn until well coated.
Roast broccolini, switching pan positions and turning with tongs halfway through cooking, until florets are browned and crisp at the edges, 20 to 25 minutes. To keep it crisp, serve in a single layer on a large platter. Drizzle with oil to taste.
Roasted Broccoli: Preheat oven to 425°. Cut 2 lbs. broccoli florets in half through the stem so they'll lie flat. Divide broccoli between 2 large rimmed baking sheets. Drizzle with 1/4 cup extra-virgin olive oil and 1/2 tsp. each kosher salt and pepper and turn until well coated. Arrange florets in a single layer, flat side down, and roast until tender-crisp and beginning to brown on the bottom, 10 to 15 minutes.
Roasted Broccolini or Broccoli with Almond Parsley Pesto: Preheat oven to 350°. Spread 1/2 cup whole raw almonds in a rimmed baking pan; roast until fragrant and golden beneath the skin, about 10 minutes. In a food processor, finely chop 2 garlic cloves. Add almonds and whirl until coarsely chopped. Add 2 cups coarsely chopped flat-leaf parsley (leaves and tender stems), 1 cup extra-virgin olive oil, and 1/2 tsp. each kosher salt and red chile flakes; whirl until parsley is finely chopped. Add 1/3 cup finely shredded parmesan cheese and pulse to combine. To serve, spread a layer of pesto on a platter. In a bowl, gently toss roasted broccolini or broccoli with more pesto and arrange on platter.
Make ahead: Pesto, up to 1 day, chilled (color will darken if held longer).