Brush the melted butter evenly over the puff pastry.
Sprinkle half the sugar on the pastry, then spread it around evenly.
Using a rolling pin, roll the pastry into a 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.
Starting from the shorter edges, roll them tightly towards the middle.
Wrap in cling film and chill for about 30 minutes.
Remove the cling film and push one of the rolls directly on top of the other.
Trim off the uneven ends of the pastry, then slice 1-centimeter (½ inch) cookie rounds. They should look like smushed hearts.
Place the slices on a baking tray lined with parchment paper 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.