Preheat the oven to 375°F (190°C). Grease a muffin tin.
Prepare the pastry: Roll out the puff pastry sheet into a large rectangle. Brush with melted butter.
Add the filling: Mix sugar and cinnamon in a bowl, then sprinkle evenly over the buttered pastry.
Roll and cut: Roll the pastry tightly into a log, then slice it into 6 equal pieces.
Shape the cruffins: Place each piece into a muffin cup, cut side up.
Bake: Bake for 18-20 minutes or until golden brown and puffed.
Cool & serve: Let them cool slightly, then dust with powdered sugar. Enjoy warm!