In a medium saucepan, pour in your apple cider and bring it to a boil. Allow it to simmer until it reduces to about ⅓ cup and thickens, around 15-20 minutes.

In a large mixing bowl, whisk together egg, granulated sugar, brown sugar, melted butter, milk, and vanilla extract until smooth.

In a separate bowl, whisk together flour, baking powder, baking soda, cinnamon, nutmeg, and cardamom.

Gently fold the dry ingredients into the wet mixture, then add the cooled apple cider syrup. Stir until just combined.

Grease your donut pan and pipe the batter into each cavity about two-thirds full.

Preheat your oven to 350°F (175°C) and bake for 10-12 minutes, until springy and a toothpick comes out clean.

Let the donuts cool for 5 minutes, then brush with melted butter and roll in cinnamon sugar.