Reduce the apple cider: Stirring occasionally, simmer the apple cider in a small saucepan over low heat until you’re left with about 3/4 cup. Start checking at 10 minutes, 15 minutes, 20 minutes, etc until you have 3/4 cup. (Mine takes about 20 minutes.) Add the butter to the reduced cider and stir until melted. Set aside to cool for 10 minutes.
Preheat oven to 350°F (177°C). Spray donut pan with non-stick spray. Set aside.
Make the donuts: Whisk the flour, baking powder, baking soda, cinnamon, nutmeg, cloves, and salt together in a large bowl. Set aside.
Whisk the granulated sugar, egg, sour cream, vanilla extract, and 1/2 cup of the reduced cider/butter mixture until well combined. (Save the rest of the reduced mixture!) Pour into the dry ingredients, and mix until just combined. The batter will be slightly thick.
Spoon the batter into a large ziplock bag or pastry bag and pipe it into the donut cavities, filling about halfway.
Bake for 9-10 minutes or until the edges and tops are lightly browned. To test, poke your finger into the top of the donut. If the donut bounces back, they’re done. Cool donuts for 2 minutes then transfer to a wire rack. Re-grease the pan and bake the remaining donut batter.
Coat the donuts: Combine the granulated sugar, cinnamon, and apple pie spice together in a medium bowl. Once cool enough to handle, dunk both sides of each donut in the melted butter, then generously in the apple spice topping.
Donuts are best served immediately. Leftovers keep well covered tightly at room temperature for up to 2 days.