Pour 2 cups of apple cider into a small saucepan. Bring to a boil over medium-high heat, then reduce heat to medium-low and simmer until the cider has reduced to about 1/2 cup. This will take about 15-20 minutes. The cider will be darker and more concentrated. Set aside to cool completely.

Preheat your oven to 350°F (175°C). Lightly grease two standard 6-cavity donut pans (or one 12-cavity pan) with non-stick cooking spray or butter.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, light brown sugar, baking powder, baking soda, salt, ground cinnamon, ground nutmeg, and ground allspice until well combined.

In a separate medium mixing bowl, whisk together the 1/2 cup of cooled reduced apple cider, milk, large egg, melted butter, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients. Stir gently with a whisk or spatula until just combined. Be careful not to overmix; a few lumps are fine.

Spoon the batter into the prepared donut pans, filling each cavity about two-thirds full. For easier filling, you can transfer the batter to a piping bag (or a large zip-top bag with the corner snipped off) and pipe it into the molds.

Bake for 12-15 minutes, or until the donuts are golden brown and spring back when lightly touched. Let them cool in the pan for 5 minutes before carefully transferring them to a wire rack to cool slightly.

While the donuts are still warm, prepare the cinnamon sugar coating. In a small shallow dish, whisk together the 1/2 cup granulated sugar and 1 tablespoon ground cinnamon.

In another small dish, melt 1/4 cup of unsalted butter. Dip each warm donut into the melted butter, coating both sides, then immediately transfer it to the cinnamon sugar mixture, turning to coat evenly.

Serve the Baked Apple Cider Donuts! warm and enjoy!