Trim leafy tops and detach all stalks from the base. Cut into 2½ to 3 inch pieces. Halve any thick base pieces vertically so everything is roughly the same thickness. Pat dry with a kitchen towel to remove surface moisture. Toss with oil, salt, and pepper directly on the sheet pan or in a bowl.

Preheat oven to 425°F. Spread celery in a single layer on a rimmed sheet pan — no crowding or it will steam instead of roast. Use two pans if needed. Roast on the center rack for 18 to 28 minutes. Start checking at 18 minutes. Done when edges are browned and caramelized, cut surfaces have color, and a fork slides in with little resistance but pieces hold their shape. For deeper caramelization, push toward 25 to 28 minutes. Flip is not required, but rotate the pan halfway if your oven runs unevenly.

Roasted celery is done when edges are golden to lightly charred, the texture is fork-tender throughout, and the flavor has concentrated into something slightly sweet and savory. No internal temperature target — go by color and tenderness alone. Rest on the pan for one to two minutes before serving to let steam escape and edges firm up slightly. Serve immediately for best texture. Watch out for these common mistakes: too little heat causes steaming instead of roasting, a crowded pan leads to soggy results, and skipping the drying step before oiling prevents browning. If celery looks pale and soft at the 20-minute mark, the oven may be running cool or the pan is overcrowded.