Reduce Apple Cider: In a small saucepan over medium heat, bring 1 1/2 cups of apple cider to a gentle boil. Simmer for 12 to 15 minutes until reduced down to exactly 1/2 cup. Set aside to cool to room temperature.

Prep Oven & Donut Pans: Preheat oven to 350°F (175°C). Lightly grease two standard 6-cavity donut pans with non-stick baking spray or melted butter.

Whisk Dry Ingredients: In a large mixing bowl, whisk together flour, brown sugar, granulated sugar, baking powder, baking soda, ground cinnamon, nutmeg, allspice, and fine sea salt until thoroughly blended.

Whisk Wet & Fold: In a separate bowl, whisk together the cooled reduced apple cider, melted butter, buttermilk, eggs, and vanilla extract. Pour into the dry flour mixture and fold gently with a spatula just until no flour streaks remain. Do not overmix.

Pipe & Bake: Spoon batter into a piping bag or gallon zip-top bag and snip the corner. Pipe batter into prepared donut cavities, filling each about 3/4 full. Bake at 350°F for 10 to 12 minutes until donuts spring back lightly when pressed and a toothpick comes out clean.

Butter & Cinnamon Sugar Coat: Allow donuts to cool in the pan for 5 minutes, then invert onto a wire rack. In one shallow bowl, melt butter. In another bowl, combine granulated sugar and cinnamon. Brush each warm donut generously with melted butter, then roll in cinnamon sugar to coat evenly. Serve warm!