In a medium saucepan over medium heat, bring 2 cups of apple cider to a gentle simmer and cook it down until it thickens to about ½ cup, which should take around 15-20 minutes. Stir occasionally. Allow it to cool completely.

In a large mixing bowl, combine the cooled reduced cider with 1 cup of unsweetened applesauce and 1 cup of brown sugar. Beat with a hand mixer on medium speed until fluffy, about 2-3 minutes.

In a separate bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon of baking powder, 1 teaspoon of baking soda, 1 teaspoon of cinnamon, ½ teaspoon of nutmeg, and ½ teaspoon of ginger. Gradually add to the wet batter, folding gently until just combined.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Drop spoonfuls of dough onto sheets, spacing them 2 inches apart. Bake for 12-13 minutes until edges set and tops spring back. Cool on a wire rack.

For the buttercream, beat ½ cup of unsalted butter until creamy, then gradually add 2 cups of powdered sugar and the remaining reduced cider, mixing until light and fluffy.

Spread a layer of buttercream filling onto one flat side of a cooled cookie, place another cookie on top, pressing lightly to secure. Repeat until all are filled.

Dust the assembled whoopie pies with a sprinkle of cinnamon for an extra cozy touch.