In a small saucepan over medium heat, bring the apple cider to a boil. Continue boiling until it has reduced to approximately ½ cup. This process typically requires 15 to 18 minutes. Remove from heat and allow it to cool completely before use.

In a medium mixing bowl, whisk together the all-purpose flour, ground cinnamon, baking soda, kosher salt, and ground nutmeg. Set aside.

In a large mixing bowl, whisk together the packed brown sugar, melted unsalted butter, and granulated sugar until thoroughly combined. Add the large egg and the cooled, reduced apple cider, whisking until smooth.

Gradually add the dry ingredient mixture to the wet ingredients. Stir gently until the dough is just combined, ensuring not to overmix. Cover the bowl with plastic wrap and refrigerate for a minimum of 2 hours or up to 12 hours for optimal results.

Arrange the oven racks in the upper and lower thirds. Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.

Using a medium cookie scoop (approximately 2 tablespoons), portion the chilled dough and roll it into uniform balls. Place them on the prepared baking sheets, spacing them at least 2 inches apart. Bake for 10 to 12 minutes, rotating the baking sheets from top to bottom halfway through the baking time. Cookies are done when they appear slightly puffed and the edges are set. Allow them to cool on the baking sheets for 15 minutes.

In one small bowl, combine the melted butter with 2 tablespoons of any remaining reduced apple cider. In a separate bowl, combine the granulated sugar and ground cinnamon.

Brush the tops of each cooled cookie with the butter-cider mixture, then dip them into the cinnamon sugar mixture to coat. Allow the coating to set before serving.