Wipe mushrooms clean with a damp paper towel — don't soak them or they'll steam instead of roast. Halve or quarter larger mushrooms (portobellos, big creminis) so everything is roughly the same size; leave small ones whole. Toss in olive oil, salt, and pepper just before roasting. Spread in a single layer on a rimmed baking sheet — no crowding, or they'll steam. Roast in batches if needed.

Preheat oven to 425°F and let it fully come to temperature. Line a rimmed baking sheet with foil, or use a ceramic or glass baking dish if roasting with liquid. Spread mushrooms in a single layer with space between pieces — crowding causes steaming, not browning. Roast on a center rack for 18 to 24 minutes. Liquid pooling early is normal; it will evaporate. Stir or toss around the 10 to 12 minute mark for even browning. Thinner slices and smaller mushrooms are done near 18 minutes; larger halved or quartered pieces may need the full 24 minutes.

Mushrooms are done when edges are deeply golden, they've shrunk noticeably, and feel tender when pierced. Pan liquid should be mostly evaporated or reduced to a glossy coating. If they still look pale and wet, roast another 3–5 minutes — pulling early gives rubbery, bland results. Serve immediately. Main mistake: overcrowding the pan. Use two pans if needed. Second mistake: pulling too soon — trust the visual cues over the clock.