Pour the apple cider into a small saucepan and simmer over medium heat for about 10-15 minutes until it reduces to exactly 3/4 cup. Let it cool completely.

Preheat the oven to 350°F (175°C). Generously grease and flour a 10-cup Bundt pan or large tube pan.

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

In a large mixing bowl, beat the softened butter, granulated sugar, and brown sugar together until pale and fluffy.

Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.

Lower the mixer speed and add the dry mixture in three parts, alternating with the reduced apple cider and the buttermilk. Start and end with the flour mixture, mixing only until just combined.

Spoon the batter into the prepared pan and smooth the top with a spatula.

Bake for 45 to 55 minutes, until a wooden skewer inserted into the center comes out clean.

Let the cake cool in the pan for about 10 minutes before inverting onto a wire rack.

While the cake is still warm, brush the entire surface with the melted butter.

Generously sprinkle or press the cinnamon-sugar mixture all over the cake until fully coated.