Step 1: Simmer 2 cups of apple cider in a small saucepan over medium heat for 20-30 minutes until reduced to 1/2 cup. Let it cool completely.
Step 2: Preheat your oven to 350°F (175°C) and generously grease a 10-12 cup bundt pan.
Step 3: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
Step 4: In a large stand mixer bowl, cream the 1 cup of softened butter with the granulated and brown sugars until light and fluffy (about 3-4 minutes).
Step 5: Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.
Step 6: Gradually add the dry ingredients to the butter mixture, alternating with the cooled cider reduction and sour cream. Start and end with the flour mixture.
Step 7: Pour the batter into the prepared bundt pan and smooth the top. Bake for 45-55 minutes, or until a toothpick comes out clean.
Step 8: Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack. While still warm, brush with melted butter and coat heavily with the cinnamon-sugar mixture.