These sourdough doughnuts have an open, airy crumb that makes them flyaway light (and impossible to stop eating). They’re as comforting as a classic yeasted doughnut, but with a slight sourdough tang that balances the sweet vanilla glaze. A tangzhong slurry not only contributes to the doughnuts’ pillowy softness but also helps them stay delicious even the next day — if they last that long!
To make the tangzhong: Whisk the tangzhong ingredients in a small saucepan until no lumps remain. Place the saucepan over medium heat and cook, stirring regularly, until the mixture is thickened and paste-like and a dragged spoon or spatula leaves a trail in the bottom of the pan, 2 to 3 minutes. Remove the saucepan from the heat and scrape the tangzhong into the bowl of a stand mixer fitted with the dough hook.
To make the dough: Weigh your flour; or measure it by gently spooning it into a cup, then sweeping off any excess. Add the flour, milk, starter, sugar, egg, yeast, and salt to the tangzhong in the mixer bowl.
Mix on low speed to bring the dough together, about 1 minute, then pause to scrape the bowl. Next, mix on medium speed until the dough is smooth, sticky, and shiny, 2 to 3 minutes.
With the mixer running, add the butter 1 tablespoon at a time, mixing until fully incorporated after each addition. Once all the butter has been added, transfer the dough to a lightly greased bowl.
Cover the bowl and let the dough rise at room temperature for 1 hour, or until slightly puffy but not doubled in volume.
Transfer the bowl to the refrigerator for at least 1 hour and up to 24 hours. While the dough is chilling, gather parchment squares or cut ten 4" squares of parchment.
To shape the doughnuts: Turn the chilled dough out onto a lightly floured work surface. Use a rolling pin or your hands to gently flatten the dough to an even 1/2" thickness.
Use a floured 3 1/2" round cutter to cut out doughnuts, then use a floured 1 1/2" round cutter to cut a hole out of the center of each. Place the doughnuts on separate parchment squares (the holes can be grouped together on one square) and transfer on the parchment to a baking sheet. Cover with lightly greased plastic wrap.
Gather the dough scraps and gently reroll them to an even 1/2" thickness. Cut out more doughnuts and doughnut holes until you have 9 doughnuts and 9 doughnut holes.
Let the doughnuts rise at room temperature for 15 to 30 minutes, or until they are slightly puffy and hold an indentation when gently pressed with a floured fingertip.
To fry the doughnuts: Toward the end of the rising time, heat the oil to 325°F in a large, heavy pot. Line a baking sheet with paper towels and set a wire rack on top.
Fry 3 doughnuts at a time, using the parchment squares to carefully invert each doughnut into the hot oil (parchment side up); the parchment should quickly release – use tongs to dispose of it. (If it doesn’t release, don’t worry: It will when you flip the doughnuts.) Cook the doughnuts until they’re brown on the bottom, 1 1/2 to 2 minutes. Using a slotted spoon, turn the doughnuts over and cook until brown on the other side, another 1 1/2 to 2 minutes. Adjust the heat as necessary to keep the oil temperature between 325°F and 350°F.
Transfer the doughnuts to the wire rack to cool completely. Repeat until all the doughnuts are fried.
Fry the doughnut holes in a single batch, gently stirring and turning them constantly with the slotted spoon, until brown all over, 3 to 4 minutes. Transfer to the wire rack and let cool completely.
To make the glaze: While the doughnuts are cooling, whisk the glaze ingredients in a large bowl until smooth.
Dip the cooled doughnuts and doughnut holes into the glaze, fully coating one side, then return them to the rack to let the glaze set, about 1 minute.
Storage information: Sourdough doughnuts are best enjoyed the day they are made. Leftover doughnuts can be stored in a paper bag at room temperature for up to 1 day. They taste best when reheated in the microwave for 10 seconds.
With origins in Japan's yukone (or yudane), tangzhong is a yeast bread technique popularized across Asia by Taiwanese cookbook author Yvonne Chen. Tangzhong involves cooking some of a bread recipe’s flour in liquid prior to adding it to the remaining dough ingredients. Bringing the temperature of the flour and liquid to 65°C (149°F) pre-gelatinizes the flour’s starches, which makes them more able to retain liquid — thus enhancing the resulting bread's softness and shelf life.
