To cut parsnips: Trim tops and bottoms; peel, and slice in half crosswise to separate thick and narrow parts. Halve or quarter thick parts lengthwise, until all parsnip pieces are roughly the same size (this ensures even cooking).
Preheat oven to 450°. Peel 2 ½ pounds medium parsnips; cut as directed above.
On two large rimmed baking sheets, toss parsnips with 2 tablespoons olive oil; season with coarse salt and ground pepper. Spread in a single layer.
Roast until tender and golden brown, 25 to 30 minutes, rotating baking sheets and tossing parsnips halfway through baking time.