Start by adding the apple cider to a sauce pan over medium-low heat. Bring it to a simmer and let it simmer until it has reduced down to ½ cup, stirring occasionally. It will take some time, around 20-30 minutes. Start checking it has reached ½ cup at 20 minutes and add more time as necessary. Let the cider reduction cool before using it in the donut batter.
3 cups (720 ml) apple cider
Preheat the oven to 350 degrees.
In a medium bowl whisk together the flour, baking powder, baking soda, salt, nutmeg, cinnamon and allspice. Set aside the flour mixture.
2 ¼ cups (281 g) all purpose flour, spooned and leveled, 1 ½ teaspoon baking powder, ¼ teaspoon baking soda, ½ teaspoon salt, 1 teaspoon ground nutmeg, 1 tablespoon ground cinnamon, ¼ teaspoon ground allspice
In a large bowl cream the softened butter, granulated white sugar and light brown sugar together with an electric mixer on high speed until fluffy, about 2 minutes.
10 tablespoon (140 g) unsalted butter, softened, ¾ cup (150 g) granulated white sugar, ¾ cup (165 g) light brown sugar
Add in the eggs and vanilla and mix on medium-high speed until pale in color and fluffy, about 1 minute.
2 eggs, at room temperature, 1 teaspoon vanilla
Next add in the buttermilk, sour cream and the reduced cider and mix on low speed until combined.
½ cup (120 ml) buttermilk, at room temperature, ½ cup (124 g) sour cream, at room temperature
Add the dry ingredients to the wet ingredients and mix on low speed just until all is combined.
Grease a donut pan with nonstick spray. Transfer the donut batter to a piping bag and cut about ½ inch opening on the bottom. Pipe the batter into the donut pan until each well is a little more than ¾ full.
Bake the donuts for 12-13 minutes, or until a toothpick comes out clean from the center.
Let them cool for 5 minutes in the pan and then turn the pan over onto a wire rack to release the donuts. Let the donuts cool until cool enough to handle.