Preheat your oven to 350°F (175°C) and grease a 9x5-inch loaf pan.
In a saucepan, bring the apple cider to a boil and let it reduce to about 1/2 cup. Set aside to cool slightly.
In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until fluffy.
Add the eggs, one at a time, mixing well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the cinnamon, nutmeg, flour, baking soda, and salt.
Gradually add the dry ingredients into the wet mixture, alternating with the buttermilk, starting and ending with the dry ingredients.
Stir in the cooled, reduced apple cider until well combined.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean.
While the loaf bakes, prepare the topping by mixing the sugar and cinnamon in a bowl.
Once the loaf is done baking, let it cool in the pan for 10 minutes.
Remove from the pan and brush the top with melted butter.
Sprinkle the cinnamon sugar mixture evenly over the top and sides of the loaf.
Allow the loaf to cool completely on a wire rack before slicing.