Preheat the oven to 350 and prepare a mini muffin tin with grease. Set to the side.
Reduce the apple cider in a saucepan on medium-low heat. Reduce the cider until it is thick and has a syrup-like consistency.
Make the batter. Combine the sugar, milk, vanilla, brown sugar, egg, and cider in a large bowl and whisk to combine.
Mix in the flour, baking powder, and cinnamon.
Scoop ¾ of the batter into each muffin slot. Bake the donut holes for 8-10 minutes. When done, they should puff up and bounce back. Let them fully cool before taking them out of the pan.
Add the cooled donut holes to a plastic bag and add in the melted butter, cinnamon, and sugar. Close the bag and shake the donut holes until they are fully covered in the cinnamon and sugar. Adjust the sugar levels to your liking.