In a wide saucepan, heat the apple cider until boiling over medium-high to high heat. Boil until the cider is reduced to ½ cup and is a little syrupy. Remove from the heat to let cool slightly. It takes about 18-20 minutes on my stove.

While the cider cools, spray each donut pan cavity with cooking spray and preheat the oven to 400 degrees F.

In a large bowl, combine the flour, baking powder, baking soda, cinnamon, nutmeg and Kosher salt. Whisk to mix.

Combine the buttermilk, vegetable oil, sugar, and egg in a medium-sized bowl or large measuring cup. Whisk until fully mixed. Slowly stream in the hot cider so that the eggs don’t scramble. Once that's mixed, add the vanilla extract.

Pour the wet ingredients into the dry. Gently fold until the mixture is just combined and has made a thick batter.

Fill each of the cavities in the donut pan about halfway to 2/3rds full. You should have exactly 12 donuts. Do not overfill. I like using a pastry bag for this.

Bake the donuts at 400 degrees F for 7-8 minutes until risen and a toothpick inserted comes out clean.

Remove the pans from the oven and allow the cider donuts to cool for 5 minutes before turning them out onto a cooling rack.

Meanwhile, melt the butter in the microwave or on the stove top and transfer to a small bowl. Combine the cinnamon and sugar in a separate dish. Choose dishes deep enough to dunk donuts and flip them easily.

Once the donuts are cool enough to handle, but still warm, dunk both sides of each donut in melted butter, letting any excess drip off back into the dish. Move the buttered donut to the cinnamon sugar bowl and generously sprinkle with cinnamon sugar, flipping to cover both sides. Repeat until the donut is well coated in cinnamon sugar, shaking off the excess. 

Transfer the coated cider donuts to a wire rack to sit and repeat the process until all the donuts are coated with butter and cinnamon sugar. Enjoy immediately.