Reduce the cider. Pour 1 1/2 cups apple cider into a small saucepan. Simmer over medium heat until reduced to about 1/2 cup, 15–20 minutes. Cool to room temperature. This step packs in the apple flavor.

Prep the pan and oven. Heat oven to 350°F (175°C). Lightly grease two 6-cavity donut pans or one pan and bake in two rounds.

Mix dry ingredients. In a large bowl, whisk flour, baking powder, baking soda, cinnamon, nutmeg, and salt until evenly combined.

Whisk wet ingredients. In another bowl, whisk the granulated sugar, brown sugar, eggs, melted butter, buttermilk, vanilla, and cooled reduced cider until smooth.

Combine. Pour wet ingredients into dry. Stir gently with a spatula until just combined. Do not overmix—a few small lumps are fine.

Fill the pans. Transfer batter to a piping bag or a zip-top bag with a corner snipped. Pipe the batter evenly into the greased donut wells, filling each about 3/4 full.

Bake. Bake for 10–12 minutes, or until the tops spring back when touched and a toothpick comes out clean.

Cool briefly. Let donuts rest in the pan for 5 minutes, then turn out onto a wire rack.

Coat. Stir together sugar and cinnamon in a shallow bowl. If using melted butter, brush it lightly over warm donuts. Dip each donut in the cinnamon-sugar, turning to coat all sides.

Serve. Enjoy warm, or let them cool fully for a slightly firmer texture and a crisp sugar crust.