01 - Preheat the oven to 350°F. Grease a standard donut pan thoroughly to prevent sticking.
02 - Simmer apple cider in a small saucepan over medium heat until it reduces to 1/2 cup, approximately 7 to 10 minutes. Allow to cool to room temperature.
03 - In a large mixing bowl, whisk together all-purpose flour, granulated sugar, brown sugar, baking powder, baking soda, cinnamon, nutmeg, allspice, and salt until evenly blended.
04 - In a separate bowl, whisk the cooled reduced apple cider, melted butter, whole milk, eggs, and vanilla extract until smooth and homogeneous.
05 - Add the wet mixture to the dry ingredients and gently fold together until just combined, taking care to avoid overmixing to maintain tender texture.
06 - Spoon or pipe batter into the prepared donut pan cavities, filling each about 3/4 full for proper rise.
07 - Bake in the preheated oven for 12 to 15 minutes until donuts are golden and a toothpick inserted in the center comes out clean.
08 - Allow donuts to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
09 - Combine granulated sugar and cinnamon in a shallow dish. Brush each cooled donut with melted butter, then dip into the cinnamon-sugar mixture to evenly coat.