**Reduce the Apple Cider**: In a saucepan over medium-low heat, simmer the apple cider until it reduces to ½ cup, stirring occasionally. This will take about 20-30 minutes. Let it cool before using.

**Preheat Oven**: Preheat the oven to 350°F.

**Mix Dry Ingredients**: In a medium bowl, whisk together the flour, baking powder, baking soda, salt, nutmeg, cinnamon, and allspice. Set aside.

**Cream Butter and Sugars**: In a large bowl, use an electric mixer to cream the softened butter, granulated sugar, and light brown sugar on high speed until fluffy, about 2 minutes.

**Add Eggs and Vanilla**: Add the eggs and vanilla, mixing on medium-high speed until pale and fluffy, about 1 minute.

**Combine Wet Ingredients**: Add the buttermilk, sour cream, and reduced cider to the mixture, mixing on low speed until combined.

**Mix in Dry Ingredients**: Gradually add the dry ingredients to the wet mixture, mixing on low speed until just combined.

**Prepare Donut Pan**: Grease a donut pan with nonstick spray. Transfer the batter to a piping bag, cutting a ½ inch opening at the bottom. Pipe the batter into the pan until each well is slightly more than ¾ full.

**Bake**: Bake the donuts for 12-13 minutes, or until a toothpick comes out clean.

**Cool**: Let the donuts cool in the pan for 5 minutes, then transfer them to a wire rack to cool until they can be handled.

**Melt Butter**: Melt the butter in a small bowl.

**Mix Spiced Sugar**: In a separate bowl, mix the granulated sugar, cinnamon, nutmeg, and allspice.

**Coat Donuts**: Using a pastry brush, brush each donut with melted butter, then roll them in the spiced sugar mixture. Serve right away!