01 -
Start by warming the milk over low heat in a pot. Whisk the egg yolks, sugar, vanilla, and flour in a mixing bowl until it looks pale and smooth. Slowly pour the warm milk into the bowl while stirring non-stop. Pour everything back into the pot, and cook on medium, stirring until it thickens. Move it to a bowl, cover it up, and chill for an hour.
02 -
Turn your oven to 400°F (200°C). Spread out the thawed pastry on a surface coated lightly with sugar, making a 9x12 inch rectangle. Slice it into 12 even pieces. Take each piece and wrap it around a horn mold, overlapping as you wrap. Place the molds seam-side down onto a baking sheet covered with parchment. Brush them with the beaten egg combined with a little water. Bake until they turn golden, about 15-20 minutes. Let them cool a bit before taking off the molds.
03 -
Once the pastry shells are cool, pipe the chilled custard into each one using a piping bag. Dust the tops with some powdered sugar, and they're ready to eat.