1. Set the oven temperature to 400°F (200°C) in advance.
Sprinkle sugar over the counter and puff pastry, then use a rolling pin to flatten it into a rectangle approximately 9 by 12 inches in size.
Divide the pastry into 12 strips, each about 1 inch thick. To simplify the process, you could divide the pastry into three parts and then slice each part into four strips.
Wrap each strip around a conical horn mold, making sure the pastry overlaps by about half its length.
Make sure the seam side is facing downwards as you place the pastry strips on a baking sheet that has been lined with parchment paper.
Mix one egg and one tablespoon of water by vigorously whisking them together. Lightly brush the surface of each pastry cone with the egg wash.
Take care to avoid getting the egg wash on the mold, as this will make it more difficult to remove the baked pastry horn from the mold.
Bake the pastry horns at 400°F (200°C) for approximately 15-20 minutes, or until the tops are golden in color.
After letting the pastries cool for a few minutes, extract them from the mold carefully. If the pastry sticks to the mold, you may compress the mold slightly (to reduce its circumference) and carefully rotate it within the pastry until it releases.
Using a piping bag, fill the pastries with cream prior to serving. If desired, sprinkle them with powdered sugar, then savor and delight in their taste!