Step 1: Simmer the apple cider in a small saucepan over medium heat for about 20 minutes until it reduces to 1 cup. Let it cool completely.
Step 2: Preheat your oven to 350°F (175°C) and grease a mini-muffin tin thoroughly with non-stick spray or butter.
Step 3: In a medium bowl, whisk together the flour, baking powder, baking soda, 1 tsp cinnamon, nutmeg, and salt. Set aside.
Step 4: In a large bowl, cream together 1/2 cup softened butter, 1/2 cup granulated sugar, and brown sugar until light and fluffy. Beat in the egg, then stir in the cooled cider reduction and buttermilk.
Step 5: Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Do not overmix the cinnamon sugar apple cider donut holes batter.
Step 6: Fill each mini-muffin cup about 3/4 full with batter. Bake for 10-12 minutes or until a toothpick comes out clean.
Step 7: While baking, prepare the coating by melting 1/2 cup butter in one bowl and mixing the remaining sugar and cinnamon in another.
Step 8: Once baked, let the cinnamon sugar apple cider donut holes cool for 2 minutes. Dip each hole into the melted butter, then roll generously in the cinnamon-sugar mixture.