Heat a large shallow pot over medium heat. Add the brown sugar and onion, and cook for about 10 minutes, stirring occasionally, until the onions are soft and the sugar is caramelizing.
Add the salmon to the pan, skin side down. Add the bay leaves, raisins, and lemon juice. Then add enough water to come about halfway up the sides of the fillets.
Cover the pot and bring to a boil over high heat. Reduce to a simmer and cook for exactly 17 minutes. Do not overcook.
Uncover the pot and let the fish cool completely before transferring it to a glass or other non-reactive container. Refrigerate for at least five hours, or up to a few days. (Or, freeze for up to a few weeks.)