Reduce apple cider:

Heat the apple cider to a boil, then reduce to medium and let it simmer until it reduces to 1/3 cup, roughly 15-18 minutes. Take off heat and allow to reach room temperature.

Preheat and butter pans:

Set oven to 350F. Butter two 6-well donut pans.

Whisk dry ingredients:

Combine all dry ingredients in a bowl and whisk.

Mix wet ingredients with cider:

In a separate bowl, whisk together all wet ingredients. Add the cooled cider and mix in.

Fold dry into wet:

Pour the dry mixture into the wet. Use a silicone spatula to fold together with a few quick motions.

Fill piping bag:

Transfer batter to a large zip-top bag, pushing it to the bottom. Squeeze out air, seal, then cut about a 3/4 inch tip from one lower corner.

Pipe batter into pans:

Pipe batter into the donut wells, filling each slightly over halfway.

Bake donuts:

Bake for 9-11 minutes until the donuts feel firm when touched.

Cool donuts on rack:

Flip donuts onto a wire rack to cool while preparing the topping.

Prepare cinnamon sugar:

Melt the butter. In a bowl big enough for a donut, stir together the sugar, cinnamon, and nutmeg.

Coat donuts with butter and sugar:

Brush melted butter onto a donut, then roll it in the sugar mixture, pressing lightly so it sticks. Do the same for all donuts.