Jamaicans have used salt mackerel for hundreds of years in a well-known dish called "mackerel run down." The "run down" aspect comes from the slow cooking, or cooking the fish until it has been literally "run down," or made tender and juicy by the slow cooking process. You don't have to fly to Jamaica to enjoy a taste of the island at home, however. If you can find salt mackerel in the grocery store, you can recreate this Jamaican favorite in your own kitchen.
Soak the mackerel overnight in cool water in a bowl in your refrigerator. This will remove some of the salt and make it taste more fresh.
Take the mackerel out of the refrigerator. Fill a large saucepan with cool water and bring it to a boil over high heat on the stove top. Add the mackerel and boil them for 15 minutes. This removes any lingering traces of salt. Remove the fish from the water with a skimmer and allow it to cool until you can easily handle it.
Remove the heads and bones. Chop the fish into 2-inch strips width-wise.
Pour the coconut milk into the saucepan and bring it to a boil. Reduce the heat to medium and add the onion, scallion, tomatoes, garlic, thyme, sea salt and fresh ground pepper, and Scotch bonnet peppers, if you are using them. Simmer the ingredients for 10 minutes to blend the flavors.
Add the mackerel and simmer it for 20 minutes, or until it is opaque all the way through and tender. Serve the mackerel hot.
If you would like to reserve the cooking liquid and make a sauce, remove 1/4 cup of the broth left in the pot after the mackerel has been removed. Whisk in 1 tbsp. flour with the 1/4 cup broth and add it to the liquid left in the saucepan. Simmer, whisking constantly, until the sauce has reduced to your desired consistency. Serve the sauce hot over the mackerel.