In a small saucepan over medium-low heat, simmer 1 1/2 cups of fresh apple cider for 15-20 minutes until reduced to exactly 1/2 cup of concentrated amber syrup. Allow to cool for 10 minutes.

Preheat oven to 350°F (175°C). Generously grease two 6-cavity standard donut pans with nonstick baking spray.

In a large bowl, whisk together flour, baking powder, baking soda, ground cinnamon, nutmeg, allspice, and sea salt until combined.

In a separate medium bowl, whisk together melted butter, eggs, brown sugar, granulated sugar, vanilla extract, buttermilk, and the reduced apple cider until smooth.

Pour the wet ingredients into the dry mixture and stir gently with a rubber spatula just until combined. Do not overmix.

Transfer batter to a piping bag (or gallon zip-top bag with the corner snipped off) and pipe evenly into donut cavities, filling each about 3/4 full.

Bake for 10 to 12 minutes until donuts are lightly golden and spring back when gently pressed. Cool in the pan for 5 minutes, then transfer to a wire cooling rack.

In a shallow dish, stir together granulated sugar and cinnamon. In another bowl, have melted butter ready. While donuts are still warm, brush all sides generously with melted butter, then toss in cinnamon sugar to coat evenly. Serve warm!