Pour 1 cup of fresh apple cider into a small saucepan. Bring to a boil over medium-high heat, then reduce to a steady simmer. Cook, stirring occasionally, for 15–18 minutes until the cider has reduced to approximately ¼ cup. It should look darker and slightly syrupy. Pour into a small bowl and let cool completely — this step can be done up to a day ahead.

While the cider cools, preheat your oven to 350°F (175°C). Generously grease a 12-cavity donut pan with non-stick spray or softened butter. Set aside.

In a large bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and allspice until evenly combined. Set aside.

In a medium bowl, whisk together the brown sugar, eggs, sour cream, melted butter, vanilla extract, and the cooled reduced apple cider until smooth and well combined.

Pour the wet ingredients into the dry ingredients and fold gently with a rubber spatula until just combined — do not overmix. A few small lumps are completely fine. The batter will be thick.

Transfer the batter to a piping bag (or a zip-lock bag with one corner snipped off). Pipe the batter into the prepared donut pan, filling each cavity about two-thirds full to leave room for rise.

Bake for 11–13 minutes, until the donuts are set, spring back lightly when touched, and a toothpick inserted into the thickest part comes out clean. Do not overbake — they should be moist in the center.

Let the donuts cool in the pan for 3–4 minutes, then turn them out onto a wire rack.

While the donuts are cooling, melt the coating butter and pour it into a shallow bowl. In a separate shallow bowl or plate, stir together the granulated sugar and cinnamon until evenly combined.

While the donuts are still warm, brush each one all over with melted butter (or briefly dip it), then roll generously in the cinnamon sugar mixture, pressing lightly so it adheres on all sides. Set back on the wire rack.

Serve immediately for the best texture and flavor. Enjoy warm!