In a medium saucepan, pour in the apple cider and bring it to a gentle simmer. Reduce for approximately 15 minutes, stirring occasionally, until it thickens and measures about 1 cup.

In a separate pot, combine diced Granny Smith apples, unsalted butter, light brown sugar, ground cinnamon, and the cooled cider reduction. Cook for about 10 minutes until apples are soft.

Create a cornstarch slurry with a splash of water, mix it into the apple mixture to thicken, cooking briefly until bubbly, then remove from heat and let cool.

In a large mixing bowl, whisk together cake flour, baking powder, ground cinnamon, and nutmeg. In another bowl, cream the butter and granulated sugar until light and fluffy. Add eggs and vanilla, mixing well.

Gradually combine dry ingredients with wet ingredients, alternating with the reduced cider, until fully incorporated.

Preheat oven to 350°F (175°C) and line a cupcake pan. Fill each liner halfway with the batter and bake for 18–22 minutes, or until a toothpick comes out clean. Cool in the pan for 5 minutes before transferring.

Once cooled, use a small knife to remove the center of each cupcake and fill generously with the prepared apple filling.

To prepare the frosting, beat together cream cheese and softened butter until smooth. Gradually add powdered sugar, mixing until combined. Add a bit of cider reduction, mixing until fluffy.

Frost each cupcake generously with the cream cheese frosting and sprinkle with ground cinnamon and decorate with apple slices.