Preheat the oven to 400°. On a large baking sheet, toss the broccoli florets and stems with 2 tablespoons of the olive oil and season with salt and pepper. Roast the broccoli in the oven for about 30 minutes, tossing halfway through, until browned and tender. Scrape the broccoli into a serving bowl. Add sesame seeds and sesame oil, toss well and serve.