1Vacuum-seal the skin.
2Place the bag in a sous vide water bath set at 185°F. Cook for 3 hours, until the collagen in the skin breaks down. Transfer the bag to an ice bath to cool immediately.
3Remove from bag and rinse the collagen off of the skin under cold running water. Pat dry with a towel.
4Preheat oven to 330°F.
5Place skin on a sheet pan lined with a Silpat mat. Brush both sides of the skin with vegetable oil. Season with salt. Place the skin under the Silpat mat and stack another sheet pan on top of the Silpat. Weigh down the top sheet pan with an oven-proof pot or clean oven brick.
6Bake for 30-50 minutes, until the skin is flat and crispy, checking the skin every 5 minutes starting at the 30-minute mark. (Cook time depends on the thickness of the fish skin.)
7Remove from the Silpat and allow the skin to cool for 20 minutes before handling.