01 -
Warm the milk in a saucepan until steaming but not boiling. In a bowl, whisk the egg yolks, sugar, cornstarch, and salt until smooth. Slowly whisk in half of the hot milk, then return the mixture to the saucepan.
02 -
Cook over medium heat, whisking constantly, until the custard thickens and bubbles, 3-5 minutes. Remove from the heat and whisk in the vanilla and butter. Transfer to a bowl, press plastic wrap directly on the surface, and chill for at least 1 hour.
03 -
Heat the oven to 400°F (200°C). Line a baking sheet with parchment paper. Lightly grease 12 cream horn molds. Mix the beaten egg with 1 tablespoon water for egg wash.
04 -
Unfold the cold puff pastry on a lightly floured surface and roll just enough to smooth the seams. Brush lightly with egg wash, then cut into 12 long strips about 3/4 inch wide. Wrap each strip around a mold, overlapping slightly, and place seam side down.
05 -
Sprinkle the wrapped pastry lightly with powdered sugar. Bake for 18-20 minutes, until puffed and golden brown. Cool for 5 minutes, then gently twist and remove the molds. Cool the shells completely.
06 -
Whisk the chilled pastry cream until smooth, then spoon it into a piping bag fitted with a round tip. Pipe cream into each cooled shell. Dust with powdered sugar and serve soon after filling.