Bring the apple cider to a boil in a small saucepan over medium-high heat, stirring occasionally. Let it boil until reduced to 1/4 cup (60ml)—start checking at 10, 15, and 20 minutes until you reach the right amount. Mine usually takes about 20 minutes. Let it cool for 10 minutes before using in step 4. You can also make the reduction in advance—cover and refrigerate it, then bring it to room temperature before using.
Preheat the oven to 350°F (177°C). Line two baking sheets with parchment paper or silicone baking mats. Set aside.
Whisk the flour, cinnamon, nutmeg, salt, baking powder, baking soda, and ginger in a medium bowl.
In another large bowl using a hand mixer or a stand mixer fitted with a paddle attachment, beat the butter, brown sugar, granulated sugar, on mat medium-high speed until creamed, forut 1 minute.
Beat in eggs one at a time, mixing well after each addition, then add the apple butter, cooled reduced apple cider, and vanilla extract. Mix until well combined.
Add the dry ingredients to the wet ingredients, then mix on low until completely combined. Batter will be thick and creamy.
Using a medium cookie scoop, scoop mounds of batter, about 1 and 1/2 Tablespoons each, onto prepared baking sheets about 2 inches apart. Bake the cookies for 12-14 minutes or until the edges are very lightly browned and the tops spring back when lightly touched. Remove from the oven and allow cookies to cool on the baking sheet for 5 minutes.
While the cookies are baking mix, the sugar and cinnamon for the coating in a small bowl.
Once the cookies are done, let them cool on the baking sheet for 5 minutes. Brush each cookie with melted butter and dip in the cinnamon sugar mixture.
Make the filling: In a large bowl using a handheld or stand mixer fitted with a paddle attachment, beat the cream cheese and butter until completely smooth and creamy, about 2 minutes. Add the confectioners’ sugar, marshmallow fluff, cinnamon, and vanilla extract. Then beat on medium speed until combined. Taste; if it is too sweet, add a pinch of salt.
Pair the cookies up based on their size. Spread (I just spread it on with a knife) or pipe (use Wilton 1A piping tip) the frosting onto the flat side of one cookie. Top with teaming cookies to form sandwiches. Serve immediately. Cover leftover whoopie pies and store them in the refrigerator for up to 5 days.