Start by getting your workspace ready. Gather all the ingredients, measuring cups, and mixing bowls. It’s helpful to line two baking sheets with parchment paper to make the process smoother.

Pour 1 cup of apple cider into a saucepan and simmer it over medium heat. Allow it to reduce until you’re left with about ¼ cup, which takes around 10-15 minutes. Once it’s reduced, set it aside to cool.

While your cider is cooling, preheat your oven to 350°F (175°C).

In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, nutmeg, and cloves.

In a large mixing bowl, beat the softened butter and brown sugar together until light and fluffy, about 2-3 minutes.

Add in the egg and vanilla extract, beating until combined.

Gradually mix in the reduced apple cider until well incorporated.

Add the dry ingredient mixture in three parts, alternating with the whole milk. Begin and finish with the dry ingredients, mixing only until just combined.

Drop tablespoon-sized rounds of batter onto the lined baking sheets, leaving about 2 inches between each one.

Bake for 10-12 minutes, or until firm to the touch and a toothpick inserted in the center comes out clean.

Transfer the whoopie pie halves to a wire rack to cool completely.

Beat the butter until creamy, then gradually add the powdered sugar, followed by the reduced apple cider, vanilla, and a pinch of salt. Beat until fluffy and smooth.

On the flat side of one whoopie pie half, pipe or spoon a generous amount of buttercream. Drizzle caramel on top and, if desired, sprinkle flaky sea salt.

Press the second half on top to create a sandwich. Repeat until all pies are assembled.