Reduce the cider: Pour the apple cider into a small saucepan and let it gently simmer over medium heat until it’s down to about ⅓ cup — this should take around 15–20 minutes. Set it aside to cool.

Brown the butter: In a separate small pan, melt the butter over medium heat. Keep cooking until it foams and turns a rich golden brown with that toasty, nutty smell that tells you it’s ready. Let it cool slightly.

Prep the pan: Heat your oven to 350°F (175°C) and grease your donut pan so nothing sticks.

Mix the dry ingredients: In a medium bowl, whisk together the flours, baking soda, baking powder, salt, cinnamon, nutmeg, and allspice.

Mix the wet ingredients: In a large bowl, whisk together the browned butter, brown sugar, granulated sugar, egg, cooled cider reduction, buttermilk, and vanilla. If you’re using grated apple, stir that in now.

Bring it together: Add the dry mixture to the wet and gently fold until just combined. Don’t overmix — the batter should be thick, not overworked.

Fill and bake: Transfer the batter to a piping bag (or a zip-top bag with the corner snipped) and pipe into the donut cavities, filling each about two-thirds full. Bake for 10–12 minutes, until they spring back lightly when touched.

Add the topping: While the donuts are still warm, brush them with melted butter and toss in cinnamon sugar until fully coated.