Reduce the cider: In a small saucepan over medium heat, bring 1 1/2 cups apple cider to a gentle boil. Simmer for 15-20 minutes until reduced to exactly 1/2 cup. Set aside to cool slightly.

Preheat oven & prep pans: Preheat oven to 350°F (177°C). Generously grease two standard 6-cavity donut pans with non-stick spray or softened butter.

Whisk dry & wet ingredients: In a medium bowl, whisk together flour, baking powder, baking soda, ground cinnamon, nutmeg, allspice, and salt. In a large bowl, whisk together melted butter, granulated sugar, brown sugar, eggs, buttermilk, vanilla extract, and cooled reduced apple cider until smooth. Fold dry ingredients into wet until just combined—do not overmix.

Pipe & bake: Transfer batter into a large piping bag (or gallon zip-top bag with the corner snipped off). Pipe batter evenly into the prepared donut cavities, filling each about 3/4 full. Bake at 350°F for 10-12 minutes until tops spring back gently when pressed.

Cool & crust: Allow donuts to cool in the pans for 5 minutes, then invert onto a wire rack. In a shallow bowl, mix 1 cup sugar and 1 1/2 tbsp cinnamon. Melt 1/2 cup butter in a separate bowl. While donuts are warm, dip both sides lightly in melted butter, then roll generously in the cinnamon sugar coating until encrusted. Serve warm with hot spiced cider!