Add the apple cider to a saucepan and simmer over medium heat, until it has reduced to ¾ cups. Set it aside to cool.
1 ¼ cups apple cider
While your apple cider cools, preheat your oven to 350°F. Generously grease a 10-12 cup Bundt pan with butter, ensuring you get into all the crevices. Lightly dust the pan with flour and tap out the excess. Set aside.
butter and flour for greasing the pan
Combine the flour, baking powder, baking soda, cinnamon, nutmeg, and salt in one bowl.
2 ½ cups all-purpose flour, 2 teaspoons baking powder, ½ teaspoon baking soda, 1 teaspoon ground cinnamon, ½ teaspoon ground nutmeg, ¼ teaspoon fine sea salt
In a large mixing bowl or the bowl of a stand mixer, add the softened butter, granulated sugar and brown sugar. Beat until light and fluffy, 3 to 5 minutes.
1 cup unsalted butter, 1 cup granulated sugar, ½ cup light brown sugar
Add in the vanilla extract. Gradually add in the eggs one at a time, mixing well in between each addition.
1 teaspoon vanilla extract, 3 large eggs
Mix in the sour cream. Pour in the cooled apple cider reduction and mix on low speed to combine.
¼ cup sour cream, 1 ¼ cups apple cider
Gradually add in the flour mixture about ½ cup at a time. Mix until you have a smooth consistency.
Pour the batter into the prepared bundt pan, smoothing the top with a spatula. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10-15 minutes, then carefully transfer it to a wire rack to continue cooling.
Combine the sugar and cinnamon together and melt the butter.
½ cup granulated sugar, 1 teaspoon ground cinnamon, ¼ cup unsalted butter
Once the cake has cooled slightly, but is still warm, brush the cake with the melted butter. Sprinkle the sugar mixture over the cake generously, pressing lightly to help it adhere to the butter.