In a small saucepan, simmer 1 cup of apple cider over medium heat until it reduces to ½ cup, about 10–15 minutes. Set aside to cool slightly.
Preheat oven to 350°F (175°C). Grease a 10-cup Bundt pan very well with butter or nonstick spray, making sure to get into every crevice, then lightly dust with flour.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Set aside.
In a large bowl, whisk together the oil, brown sugar, granulated sugar, eggs, and vanilla until smooth. Stir in the applesauce and reduced apple cider.
Add the dry ingredients to the wet and mix just until combined. Don’t overmix — you want a soft, tender crumb.
Pour the batter into the prepared Bundt pan and smooth out the top. Bake for 40–50 minutes, or until a toothpick inserted in the center comes out clean. Let the cake cool in the pan for 15 minutes, then carefully invert onto a wire rack.
Once the cake is warm (not hot), brush it all over with melted butter. In a small bowl, combine the granulated sugar and cinnamon, then generously sprinkle and pat it onto the cake until fully coated.