Pull the fillet from the fridge about 10 minutes before cooking to take off the chill — this helps it cook evenly. Pat the surface dry with paper towels so seasoning sticks and the fish doesn't steam. Line your baking sheet with foil then parchment on top for easy cleanup and no sticking. Season the flesh side with salt and pepper; add a drizzle of olive oil or melted butter if you like. Place skin-side down on the pan — the skin shields the flesh from the direct pan heat.

Preheat oven to 400°F and let it fully come to temperature. Place rack in the center position. Set salmon skin-side down on the baking sheet and slide it onto the center rack. Do not flip during cooking. Bake 10–15 minutes depending on thickness: thinner fillets (~¾ inch) are done around 10 minutes; thicker fillets (~1½ inches) may need the full 15. Start checking at 10 minutes. For a moist result, tent foil loosely over the fillet or fold it into a loose packet — note the top won't brown this way. Leave uncovered if you want a caramelized or glazed surface. If using a glaze or sauce, pour it over the fillet before it goes in. Avoid opening the oven door repeatedly — it drops the temperature and throws off your cook time.

Insert an instant-read thermometer into the thickest part. Pull at 125°F for a moist, slightly translucent center; cook to 145°F for fully opaque, firmer flesh. No thermometer? Press gently — flesh should flake along natural lines and look mostly opaque with a hint of translucency at the center. Rest on the pan 2–3 minutes before serving. Do not overbake — salmon carries over after leaving the oven, and anything past 145°F turns dry and chalky.