In a small saucepan, combine the piloncillo (or brown sugar), vinegar and 1/3 cup water. Bring to a gentle simmer and stir until the piloncillo dissolves. Add the chiles, garlic and ½ teaspoon salt, then simmer for a couple of minutes. Remove from the heat and cool, weighting the chiles to ensure even hydration. (If there isn’t enough liquid to cover the chiles, add a little additional vinegar and water in equal portions.) After a couple of hours, the chiles are ready to use. They will keep for months refrigerated in a sealed container.