Brown the butter: In a light-coloured, heavy saucepan over medium-low heat, melt the butter. Cook, stirring often, until the foam subsides, it smells nutty, and the milk solids turn deep golden brown, 5–7 minutes. Immediately scrape everything (fat + browned bits) into a heatproof bowl to stop the cooking. Cool 5–10 minutes.You’ll use 137 g of this browned butter in the batter; reserve the rest for dipping later. Reduce the cider and enrich: Wipe out the pan. Add 496 g (2 cups) cider and boil over medium-high, stirring occasionally, until reduced by about half (to roughly 1 cup), 10–15 minutes. Off heat, whisk in the 128 g apple butter (or applesauce). Let cool until just warm, not hot
Prep pans and oven: Heat oven to 350°F. Lightly spray the cavities of your donut pans; use a pastry brush to coat evenly and avoid pooling.
Dry mix: In a medium bowl, whisk together AP flour, whole-wheat flour, baking powder, baking soda, cinnamon, nutmeg, and salt until well combined
Start the batter with browned butter and sugars: Weigh 137 g of the cooled browned butter into a large mixing bowl. Add 198 g granulated sugar and 105 g light brown sugar; whisk until glossy and slightly thick. Whisk in the eggs one at a time, fully incorporating each before adding the next, then whisk in the vanilla. (If anything looks greasy or separated, give it 30–60 seconds of extra whisking.)
Combine wet and dry ingredients: Switch to a spatula. Stir in half the dry mix, then all of the warm (not hot) cider mixture, then the remaining dry mix. Fold just until no dry patches remain. Batter will be thick and scoopable.
Fill and bake: Transfer batter to a piping bag (or zip-top bag) and pipe each cavity about ⅔ full (aim for level rims). Tap pan gently on counter to remove any large air bubbles. Bake 8–10 minutes until domed, lightly golden, and the centres spring back when gently pressed; a toothpick should come out clean. Cool 10 minutes in the pan, then turn out onto a rack. Re-grease pans and repeat with remaining batter.
Cinnamon-sugar finish: Stir together the 132 g sugar, cinnamon, nutmeg. and optional freeze-dried apple powder. Gently re-warm the reserved browned butter until fluid. While doughnuts are warm (not hot), dip the tops in butter, let excess drip, then press into the cinnamon-sugar. For a fully coated effect, lightly brush sides with butter and toss in a shallow bowl of sugar mix.
To serve and store: Best the day they’re baked. To freeze, skip the sugar coating; cool completely, freeze airtight up to 2 months. Re-warm at 300°F (about 8 minutes), then dip into melted browned butter and sugar just before serving.