Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a bowl, whisk together the flour, baking soda, cinnamon, nutmeg, and salt.
In a large mixing bowl, cream the softened butter and brown sugar until light and fluffy.
Add the egg, apple cider, and vanilla extract to the cream mixture, beating until combined.
Gradually mix the dry ingredients into the wet mixture until just combined.
Drop tablespoon-sized amounts of batter onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 12-15 minutes or until the cookies are set and slightly golden.
Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
Once cooled, spread a generous amount of caramel sauce on the flat side of one cookie and top with another cookie to form a sandwich.
Serve the whoopie pies immediately, or refrigerate them for a firmer filling.