Melt butter at low heat. Mix sugar and cinnamon. Unroll puff pastry with baking paper. Pull the dough carefully off the baking parchment and place it on a floured work surface. Spread the dough with the liquid butter.
Sprinkle with cinnamon sugar, leaving about 1 cm of edge free. Roll up the puff pastry tightly from the short side. Wrap tightly in baking paper and place in the freezer for about 1 hour.
Line two baking trays with baking paper. Cut the dough roll into approx. 35 slices (each approx. 5 mm thick). Place the slices on the baking trays. Bake one after the other in a preheated oven (electric cooker: 175 °C/circulating air: 150 °C/gas: level 2) for about 20 minutes.
Let it cool down.