In a small heavy saucepan, bring 1.5 cups of fresh apple cider with a cinnamon stick to a gentle simmer over medium-low heat.

Simmer uncovered for 18 to 22 minutes until reduced down to exactly ½ cup of concentrated, fragrant cider syrup. Discard the cinnamon stick and allow the syrup to cool to room temperature (about 10 minutes).

Preheat your oven to 350°F (177°C). Lightly grease two 6-cavity standard donut pans with non-stick baking spray.

In a large mixing bowl, whisk together the flour, baking powder, baking soda, ground cinnamon, grated nutmeg, allspice, and salt until thoroughly combined.

In a separate medium bowl, whisk together the melted butter, brown sugar, granulated sugar, eggs, room-temperature buttermilk, vanilla extract, and cooled concentrated apple cider reduction until velvety smooth.

Pour the wet ingredients into the dry mixture. Use a silicone spatula to gently fold just until incorporated and no flour streaks remain. Do not overmix to keep the crumb ultra-tender.

Transfer batter into a large gallon zip-top bag or piping bag, snip off a ½-inch corner, and pipe the batter evenly into the greased donut pan cavities, filling each about ¾ full.

Bake at 350°F (177°C) for 10 to 12 minutes, or until the donut tops spring back when lightly touched and a toothpick inserted into the center comes out clean.

Allow donuts to cool in the pan for 5 minutes, then turn them out onto a wire cooling rack.

While the donuts are still warm, melt ½ cup of butter in a shallow bowl. In a separate wide shallow bowl, whisk together the sugar, cinnamon, and a pinch of salt.

Dip each warm donut quickly into the melted butter, coating both sides lightly, then dredge generously in the cinnamon sugar mixture until fully coated with sparkling crystals. Serve immediately warm!