To begin, make the custard cream (crema pasticcera):

• Warm the milk until it is hot (not boiling).
• Whisk the egg yolks, sugar, vanilla extract, and flour together in a medium-sized pan until the mixture is light and fluffy.
• While whisking, add the milk a little at a time, making sure there are no lumps.
• Set the pan over medium heat and keep stirring it until it starts to slowly boil.
• The cream will get thicker, so don’t let it get stuck to the bottom. Turn down the heat and cook for a few more minutes, until the sauce is as thick as you want it to be.
• Pour the cream into a glass bowl, cover it with plastic wrap, and let it cool down. Put it in the fridge for at least an hour.

For the horns of pastry:

• Preheat the oven to 400°F (200°C).
• Sprinkle sugar on the counter and the puff pastry, then roll it out into a 9-by-12-inch rectangle.
• Cut into 12 stripes (about 1 inch thick). Cut the dough into three pieces, and then cut each piece into four strips.
• Roll each piece into a horn shape (conical in shape). The pastry must touch (about half of the length).
• Place the seam side down on a baking sheet covered with parchment paper.
• Mix together one egg and a tablespoon of water. The egg wash should be used to lightly coat each pastry cone.
• Make sure the egg wash doesn’t get on the mold. It will be harder to get the baked pastry horn out of the mold.
• Bake at 400°F (200°C) for 15–20 minutes, or until the top is golden.
• Let them cool for a few minutes, then carefully take them out of the mold.
• If the pastry sticks to the mold, gently press it in (to make the circumference smaller) and turn it inside the pastry until it comes off.
• Fill with cream before serving.
• If desired, top with powdered sugar and serve.