1. Reduce the cider: Simmer 1 1/2 cups apple cider in a saucepan over medium heat until reduced to 1/2 cup, about 15 to 20 minutes; set aside to cool slightly.

2. Preheat the oven to 350°F (175°C) and grease a donut baking pan.

3. In a large bowl, whisk together the flour, baking powder, cinnamon, nutmeg, and salt.

4. In a medium bowl, whisk together the reduced cider, brown sugar, granulated sugar, melted butter, eggs, milk, and vanilla extract until smooth.

5. Pour the wet ingredients into the dry ingredients and stir gently until just combined, being careful not to overmix.

6. Transfer the batter to a piping bag or zip-top bag, snip off a corner, and pipe or spoon the batter into the donut pan, filling each cavity two-thirds full.

7. Bake for 10 to 12 minutes, or until the tops spring back when touched and a toothpick inserted comes out clean; let cool in the pan for 5 minutes.

8. Mix the cinnamon sugar coating in a bowl, then coat the warm donuts by rolling them in the mixture; serve warm or store as desired.