**Part 1: Reducing the Apple Cider**
1. Pour 1 cup of apple cider into a small saucepan.
2. Bring to a simmer over medium heat.
3. Simmer gently, uncovered, until reduced to 1/2 cup. This will concentrate the apple flavor (about 15-20 minutes).
4. Let cool completely before using in the cake batter.
**Part 2: Making the Apple Cider Cake Layers**
1. Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper or silicone baking mats.
2. In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, cloves, and salt.
3. In a large bowl (or the bowl of a stand mixer), cream together the softened butter and sugar until light and fluffy (about 3-5 minutes).
4. Beat in the eggs one at a time, then stir in the vanilla extract.
5. In a small bowl, whisk together the cooled reduced apple cider and sour cream.
6. Gradually add the dry ingredients to the wet ingredients, alternating with the apple cider mixture, beginning and ending with the dry ingredients. Mix until just combined. Do not overmix!
7. Drop rounded tablespoons of batter onto the prepared baking sheets, leaving about 2 inches between each cookie.
8. Bake for 8-10 minutes, or until the edges are lightly golden and a toothpick inserted into the center comes out clean.
9. Let the cake layers cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
**Part 3: Whipping Up the Cream Cheese Filling**
1. In a large bowl (or the bowl of a stand mixer), beat the softened cream cheese and butter until smooth and creamy.
2. Gradually add the powdered sugar, one cup at a time, beating well after each addition.
3. Stir in the vanilla extract and salt.
4. Beat until the filling is light and fluffy.
**Part 4: Assembling Your Masterpiece**
1. Once the cake layers are completely cool, match them up by size.
2. Turn one cake layer flat-side up and spread a generous amount of cream cheese filling on top.
3. Top with another cake layer, flat-side down, to create a sandwich.
4. Repeat with the remaining cake layers and filling.
5. Serve immediately or chill for later.