1/2cupAll-Purpose FlourPlus extra for dusting work surface.
2teaspoonsBaking PowderFresh.
1/4teaspoonSaltFine.
For Finishing
Powdered SugarFor dusting.
OilNeutral oil (vegetable or canola), enough for 2–3 inches depth.
Instructions
Make the custard: In a medium saucepan, combine 2 cups whole milk and 1/2 cup granulated sugar over medium heat. Stir gently until the sugar dissolves and the milk is hot and steaming but not boiling (small bubbles at the edge), about 4–6 minutes.
Temper the eggs: In a heatproof bowl, whisk 4 large egg yolks with 1/4 cup cornstarch until smooth and pale. Slowly drizzle about 1/2 cup of the warm milk into the egg mixture, whisking constantly to avoid cooking the yolks.
Cook the custard: Pour the tempered egg mixture back into the saucepan with the remaining milk. Return to medium heat and cook, whisking continuously, until the mixture thickens to a pudding-like consistency and coats the back of a spoon, about 3–6 minutes. Do not stop whisking to prevent lumps.
Finish and cool: Remove from heat and stir in 1 teaspoon vanilla extract. Transfer the custard to a shallow bowl. Press plastic wrap directly onto the surface to prevent a skin from forming. Chill until completely cool, at least 30 minutes.
Prepare the dough: In a separate bowl, whisk together 1/2 cup all-purpose flour, 2 teaspoons baking powder, and 1/4 teaspoon salt. In another bowl, beat 1/2 cup heavy cream with an electric mixer until stiff peaks form.
Form the dough: Gently fold the whipped cream into the flour mixture until a soft, slightly sticky dough forms. Handle gently—do not overmix.
Fry the doughnuts: Heat oil in a heavy deep pan to 350°F (175°C) or until a small piece of dough sizzles and rises slowly. Shape the dough into small rounds (about 1½ inches across). Fry in batches, turning once, until evenly golden brown, 2–3 minutes per side. Use a slotted spoon to transfer to a paper towel-lined tray to drain.
Fill and finish: When the doughnuts have cooled to warm or room temperature, transfer the custard to a piping bag fitted with a small round tip. Insert the tip into the side of each doughnut and squeeze until filled. Dust generously with powdered sugar before serving.
Notes
Keep oil at a steady 350°F. Custard can be made a day ahead and chilled. Fill doughnuts just before serving for best texture.