Unwrap the puff pastry. Using your hands or a rolling pin, flatten out the seams if your puff pastry has then, making an even rectangle. Brush melted butter evenly over the puff pastry. Sprinkle half of the sugar on the pastry, then spread it around evenly. Using a rolling pin, roll the pastry into a tall rectangle, pressing the sugar into the pastry. Flip the pastry, then repeat the process, brushing with butter and rolling in the rest of the sugar.
Tightly roll the bottom of the pastry toward the middle, stopping at the center, then roll the top of the pastry to meet in the centre as well. The rolls should be the same size. Wrap in plastic wrap and chill for about 30 minutes.
Preheat the oven to 425°F (220°C). Line a baking sheet with parchment paper.
Remove the plastic wrap and push one of the rolls directly on top of the other. Trim off the uneven ends of the pastry, then slice into ½-inch (1 cm) rounds. They should look like smushed hearts. Place the slices on the baking sheet about 2 inches (5 cm) apart to allow for expansion. Bake for 15 minutes, flipping them halfway, until the sugar is caramelized and the cookies are golden brown.