Step 1In a medium bowl, combine the salt, sugar, ginger, lemongrass and peppercorns. Set aside.
Step 2Brush the top of the sable fillet generously with the sake.
Step 3Spread the cure mix over the top (flesh side) of the fillet, then wrap the fish tightly with cheesecloth. Place the wrapped sable, skin side down, on a rack over a rimmed baking sheet to catch any juices.
Step 4Refrigerate the fillet until it is firm to the touch, about 48 hours (timing will vary depending on the thickness and size of the fillet). Uncover the fillet, rinse and dry off. The cured sable will keep for up to several days, wrapped in dry parchment and refrigerated.