Apple cider: 1 cup reduced to about 1/3 cup (cool slightly before using)
Gluten-free 1:1 baking flour (with xanthan gum): 1 1/2 cups
Baking powder: 1 1/2 teaspoons
Fine sea salt: 1/2 teaspoon
Ground cinnamon: 1 1/2 teaspoons (plus 1 to 1 1/2 teaspoons for coating)
Ground nutmeg: 1/4 teaspoon
Ground cardamom: 1/4 teaspoon
Granulated sugar: 1/2 cup (plus 1/2 cup for coating)
Large egg: 1
Milk (dairy or non-dairy): 1/2 cup
Melted butter or neutral oil: 1/4 cup (plus about 2 tablespoons for brushing donuts before coating)
Optional glaze: powdered sugar 1 cup + 2 to 3 tablespoons reduced cider
Simmer 1 cup fresh apple cider in a small saucepan until reduced to about 1/3 cup (10 to 12 minutes). Cool slightly.
Preheat oven to 350°F (175°C). Grease a 6- or 12-cavity donut pan.
Whisk together gluten-free flour, baking powder, salt, 1 1/2 teaspoons cinnamon, nutmeg, and cardamom in a bowl.
In another bowl, whisk sugar and egg until smooth. Whisk in the warm reduced cider, milk, and melted butter or oil until glossy.
Add dry ingredients to wet and whisk just until uniform. Transfer batter to a piping bag or zip-top bag and snip the corner.
Pipe batter into donut cavities until about 3/4 full. Tap the pan once to settle. Bake 10 to 12 minutes, until tops spring back lightly.
Let donuts rest in the pan for 3 minutes, then transfer to a wire rack.
Stir together 1/2 cup granulated sugar with 1 to 1 1/2 teaspoons cinnamon in a shallow bowl. Lightly brush warm donuts with melted butter or neutral oil, then toss in cinnamon sugar to coat.
For a glaze, mix 1 cup powdered sugar with 2 to 3 tablespoons reduced cider until smooth. Dip cooled donuts and let set.
Serve warm. Store cooled donuts airtight up to 2 days, or freeze uncoated up to 2 months. Rewarm at 300°F for 6 to 8 minutes and coat before serving.
