Pat the fillet dry with paper towels and season generously with salt all over. Add aromatics to the bag if desired — dill, lemon zest, red pepper flakes, and a drizzle of olive oil work well. Leave the skin on if present. Place the fillet in a vacuum-seal or sturdy zip-top bag. Vacuum-seal, or use the water-displacement method: partially close the zip-top bag, lower it into the water bath to push out air, then seal fully just before submerging. The bag must stay fully submerged throughout cooking to ensure even results.

Clip your circulator to a tall pot and fill with warm water to the manufacturer's marked level. Set to 122°F for silky, buttery, translucent salmon. For a firmer flake, raise in 5°F steps — 125°F is a common sweet spot, 130°F gives a fully set texture. Do not exceed 130°F or the fish turns dry and chalky. Once water hits your target temp, lower the sealed bag in. Clip a resealable bag to the pot rim opposite the circulator outlet to keep it submerged. Weight down a vacuum-sealed bag if it floats. Confirm everything is fully submerged. Cook time: 30–45 min at 122–125°F for a fresh fillet 1–1.5 inches thick; up to 60 min for thicker cuts; ~70 min from frozen. Done when opaque outside, slightly translucent and deeply tender at the center, yielding easily when pressed through the bag. Remove when no firm or raw center remains.

Remove the bag, open carefully, and lift the salmon out gently — it's very delicate. Plate immediately and spoon bag juices over the top. Fish is fully cooked and safe to eat as-is. For crispy skin: pat skin completely dry with paper towels. Heat oil in a skillet over high heat until shimmering. Press skin-side down for 30 seconds, then sear 2–3 minutes until golden and crisp. Do not flip. Make-ahead: refrigerate sealed bag up to 4 days. Reheat in a 100°F water bath for 1 hour. Always keep bag fully submerged during cooking to avoid uneven results.