Pour the apple cider into a shallow but wide saucepan and bring to a simmer over medium heat. Simmer until reduced to ½ cup. Remove from the heat and allow it to cool. This should take about 25 minutes depending on the size of the saucepan (wider bottom allows it to evaporate more quickly). 2 cups apple cider
In a large bowl, whisk together the brown sugar, granulated sugar, vegetable oil, egg, vanilla and cooled apple cider reduction until well combined. ½ cup packed light brown sugar, ¼ cup granulated sugar, ½ cup vegetable oil, 1 large egg, 1 teaspoon vanilla extract
Add the flour, baking soda, baking powder, salt, cinnamon, nutmeg and cardamom to the same bowl. Stir just until combined. Do not overmix. 2 cups all-purpose flour, 1 teaspoon baking soda, ½ teaspoon baking powder, ½ teaspoon salt, 1½ teaspoons ground cinnamon, ¼ teaspoon ground nutmeg, ⅛ teaspoon ground cardamom
Allow the batter to rest for 10 minutes while the oven preheats to 350°F. Grease the cavities of the donut pans with cooking spray.
Spoon the batter into a decorating bag or large zippered bag. Snip off one corner and pipe the batter into the prepared donut pans, filling each cavity about ¾ full.
Bake for 10–12 minutes, or until the tops spring back when lightly touched. Allow the donuts to cool in the pans for 2–3 minutes, then transfer them to a wire rack.
In a shallow bowl, mix together the granulated sugar, finely crushed apple cider drink mix and cinnamon. Place the melted butter in a separate bowl. ⅔ cup granulated sugar, 1 packet spiced apple cider drink mix, 1½ teaspoons ground cinnamon, ⅔ cup salted butter
While the donuts are still warm, brush each one all over with melted butter, then roll in the apple cider sugar mixture until completely coated. For a thicker coating, let the donuts sit for 5 minutes, then repeat the butter and sugar coating.
Notes
Apple cider: Use regular apple cider, not apple cider vinegar. Reduce the cider to exactly ½ cup for concentrated apple flavor without adding too much liquid to the batter.
Make ahead: The apple cider can be reduced ahead of time and stored in the refrigerator until ready to use.
Measure the flour: For the best texture, weigh the flour with a kitchen scale. Too much flour can make the donuts dry.
Don't overmix: Stir the batter just until the dry ingredients are incorporated to keep the donuts soft and tender.
Donut pans: Fill each cavity about ¾ full to give the donuts room to rise without overflowing.
Storage: Store leftover donuts in an airtight container at room temperature for up to 2 days. The cinnamon sugar coating may soften as they sit.