01 -
Heat the milk in a saucepan until steaming. In a bowl, whisk egg yolks, sugar, cornstarch, and salt until smooth. Slowly whisk in the hot milk, then return the mixture to the saucepan and cook over medium heat, whisking constantly, until thick and bubbling, 2-4 minutes.
02 -
Remove the custard from the heat and whisk in butter, vanilla, and lemon zest. Press plastic wrap directly on the surface and refrigerate until cold, at least 1 hour.
03 -
Heat the oven to 425°F. Line two baking sheets with parchment. In a medium saucepan, bring water, milk, butter, sugar, and salt to a full boil.
04 -
Add the flour all at once and stir firmly with a wooden spoon until the dough pulls from the sides of the pan and leaves a light film on the bottom, about 1-2 minutes.
05 -
Transfer the dough to a mixing bowl and cool for 5 minutes. Beat in the eggs one at a time, mixing well after each addition, until the dough is glossy and slowly drops from the spoon.
06 -
Pipe 18 mounds onto the prepared pans, spacing them about 2 inches apart. Bake for 15 minutes, then reduce the oven to 350°F and bake 15-18 minutes more, until deeply golden and dry-looking.
07 -
Pierce each puff with a skewer or small knife. Return them to the turned-off oven with the door cracked for 5 minutes, then cool completely on a rack.
08 -
Whisk the chilled custard until smooth. Pipe it into the bottoms of the puffs or split the shells and spoon it inside. Dust with powdered sugar just before serving.