Make the cookies: In a small saucepan, combine the butter, molasses, brown sugar, cinnamon, nutmeg, mace, cloves, and salt. Warm the mixture over medium-low heat, stirring with a silicone spatula, until the butter has melted and the sugar has dissolved, about 3 minutes. Bring to a simmer over medium heat and cook, stirring constantly, for 5 seconds, then remove then pan from the heat and let cool for 5 minutes. Meanwhile, crack the egg into a small bowl, whisk it well, and weigh out 1 ounce into a second small bowl; discard the remainder or reserve for another use.

Whisk a bit of the hot butter-sugar mixture into the egg to temper it, then whisk the mixture back into the saucepan, scraping the bowl with the spatula; set aside.

In a large bowl, whisk together the flour, baking powder and baking soda. Add the citron and currants, then toss until evenly distributed and well coated with the flour. Pour the liquid ingredients into the dry, scraping the pan to get every drop, then stir briskly with a spatula or wooden spoon until well combined; the resulting dough will be quite soft and sticky. Let the dough rest, uncovered, for 15 minutes (fig. 3.1).

Cut two 9 by 6-inch pieces of parchment paper. With a plastic dough scraper, divide the dough in half (about 7.2 ounces each) and drop each half horizontally onto one of the parchment sheets, forming it into a rough log along the center of the sheet. Moisten your hands with water and shape each piece of dough into a 7-inch cylinder about 1 inch in diameter (fig. 4.1). Tightly roll up each cylinder in the parchment, using a small metal spatula to tidy the dough and push it back toward the beginning of the roll (fig. 4.2), then twist the ends of the paper like a candy wrapper (fig. 4.3). Refrigerate for at least 2 hours or up to overnight.

When you are ready to bake, adjust an oven rack to the middle position and heat the oven to 350 degrees. Line a rimmed baking sheet with parchment paper. Unwrap the dough logs and transfer them to the prepared baking sheet (fig. 5.1), spacing them about 2 inches apart. Bake until the the cylinders have broadened and formed fissures but still feel soft on top (fig. 5.2), about 20 minutes, rotating the baking sheet halfway through. Let cool on the baking sheet on a wire rack for about 5 minutes, then transfer the logs directly to the rack and let cool completely. Using a serrated knife, cut each log crosswise into 1½-inch sections.

Make and apply the icing: In a small bowl, whisk together the confectioners’ sugar, milk, and vanilla until the mixture forms a heavy glaze. Using a fork, drizzle the glaze onto the cookies; alternatively, use a parchment cone to pipe it on. Let the icing dry completely, about 20 minutes. The hermits will keep for up to 3 weeks in an airtight container at room temperature.