Position a rack in the center of the oven and heat the oven to 475° F. Line a heavy-duty rimmed baking sheet with parchment. Trim and peel the broccoli stem; slice it into 1/4-inch-thick disks. Where the stem starts to branch out, split the florets though the stem so that each piece is 1-1/2 to 2 inches wide. In a medium bowl, toss the broccoli with enough of the olive oil to coat generously, the salt, and a few grinds of pepper.
Turn the broccoli out onto the baking sheet and arrange the pieces so that they are evenly spaced. If the pieces cover the baking sheet sparsely, arrange them toward the edges of the baking sheet for the best browning. Roast until the floret tops begin to brown, 8 to 10 minutes. Stir and continue to roast until tender, 3 to 6 minutes.
Return the broccoli florets to the bowl in which you tossed them with the oil, or put them in a clean serving bowl. If they seem a bit dry, drizzle them with a little more oil. Season to taste with salt, pepper, and lemon juice, if using.