01 -
Heat milk until steaming but don't let it bubble over. Whip up egg yolks with sugar, vanilla, and flour until smooth. Slowly add the hot milk while stirring. Simmer on medium, stirring nonstop, until it thickens. Chill in the fridge for no less than an hour.
02 -
Turn oven on to 400°F. Spread out puff pastry, sprinkle some sugar, and roll to about 9x12 inches. Slice into 12 slim strips, each about an inch wide.
03 -
Wrap each pastry strip around a horn mold, slightly overlapping as you go. Put them seam-side down on parchment-lined pans.
04 -
Mix egg with a bit (1 tablespoon) of water. Lightly coat the pastry tops without touching the molds.
05 -
Pop them in the oven at 400°F for 15-20 minutes until they're golden brown. After cooling briefly, carefully slide off the molds.
06 -
Stuff the cooled pastry horns with custard using a piping bag. Sprinkle powdered sugar on top before enjoying.