Preheat the oven to 190ºC and line a baking sheet with baking paper.
Mix the sugar and cinnamon (if using) in a bowl.
Unroll the puff pastry onto the lined baking sheet, and sprinkle the sugar mix onto the pastry, covering the whole surface evenly.
On the long side, carefully roll the pastry into a tight roll, and stop when you get to the middle. Repeat on the other side until the two rolls meet in the middle.
Wrap it up in the baking paper and refrigerate for about 10 minutes so that it firms up.
Remove from the fridge and unwrap, then carefully slice into ½-1 cm thick rounds with a sharp knife.
Place onto the lined baking sheet a couple centimetres apart.
Bake for 10-12 minutes until golden. Remove and cool before serving – and store the leftovers in an airtight container.