Reduce the Apple Cider
In a small saucepan, bring 1 cup of apple cider to a gentle boil. Simmer until it reduces to ¼ cup, about 15–20 minutes. Cool completely before using.

Make the Whoopie Pie Batter
In a medium bowl, whisk together flour, baking soda, baking powder, salt, cinnamon, nutmeg, and cloves. Set aside. In a large bowl, beat the softened butter and brown sugar until light and fluffy (about 2 minutes). Add the egg and vanilla, beating well to combine.

Combine Wet and Dry
Mix in the cooled reduced cider. Alternate adding dry ingredients and milk, beginning and ending with dry, until the batter is smooth and thick.

Scoop and Bake
Preheat the oven to 350°F (175°C). Line baking sheets with parchment paper. Drop rounded tablespoons of batter about 2 inches apart. Bake for 10–12 minutes or until tops spring back when touched. Let cool completely on wire racks.

Prepare the Buttercream
Beat softened butter until creamy. Gradually add powdered sugar, mixing well. Add the reduced cider, vanilla, and salt. Beat until smooth and fluffy.

Assemble the Whoopie Pies
Spread or pipe a ring of apple cider buttercream on the flat side of one cake. Spoon a bit of caramel in the center. Top with a second cake to make a sandwich. Repeat with remaining cakes.

Optional Finishing Touch
Sprinkle a pinch of flaky sea salt on the exposed caramel for added flavor contrast.