Why high heat works
Vegetables are mostly water, and nothing browns until the water on its surface has gone. At 425 degrees that happens quickly, so the outside caramelizes while the inside turns tender. At 350 the same vegetable softens long before it colors, and you end up with something limp and pale that tastes boiled. The whole craft of roasting is getting moisture out of the way, which is why the pan, the spacing and the towel matter as much as the oven.
The method
- Heat the oven to 425 degrees with a rack in the lower-middle position, and wait until it has fully preheated.
- Cut the vegetables into even pieces, about one inch across, so that they finish at the same moment.
- Dry them thoroughly with a towel after washing, because wet vegetables steam.
- Toss them in a bowl with about one tablespoon of oil and half a teaspoon of kosher salt per pound, until every surface has a thin gloss.
- Spread them on a heavy rimmed sheet pan in a single layer, cut sides down, with visible space between the pieces. Use a second pan before you crowd the first.
- Roast until the undersides are deep brown, turn them once, and continue until a knife slides in without resistance.
Times by vegetable
- Asparagus, green beans and cherry tomatoes take 10 to 15 minutes.
- Broccoli, cauliflower, zucchini, peppers and mushrooms take 20 to 25 minutes.
- Halved Brussels sprouts and onion wedges take 25 to 30 minutes.
- Potatoes, sweet potatoes, carrots, beets and winter squash take 35 to 45 minutes.
For a mixed pan, start the slow vegetables first and add the quick ones partway through, or give each kind its own pan and pull them as they finish.
Mistakes and finishes
Minced garlic and fresh herbs burn at this temperature, so add garlic for the last ten minutes and herbs after the pan comes out. Thin, flimsy pans warp and scorch. Too little oil gives you leathery edges instead of crisp ones. Parchment is fine for easy cleanup, although bare metal browns better. When the vegetables come out, finish them with something sharp or rich: a squeeze of lemon, a splash of vinegar, a grating of hard cheese or a spoonful of yogurt.
Tip Put the empty sheet pan in the oven while it heats. Vegetables that land on hot metal begin browning on contact, which does more for potatoes than any other trick.
