Dress and debone the smelt. Mix the salt, brown sugar, coriander, chile powder, and mace together to combine. Sprinkle salt blend evenly all over the flesh side of the fish. Stack the fish, flesh to skin. Allow to sit overnight in the refrigerator.
Gently rinse the fish under cold water—not vigorously enough to remove all the spices, but just enough to get the remaining chunks of salt off. Pat dry.
Layer the fish in a shallow, heatproof container.
Place vinegar, water, shallot, and bay leaf in a small sauce pot and bring to a boil.
Pour the hot pickle over the smelt, making sure they are fully submerged. Marinate for at least 2 hours, or up to 6 hours.
If using the fish the day of, remove from the pickle just before needed. To store the fish for up to a week, remove them from the pickle and cover in olive oil. Keep refrigerated.