Prepare the Crème Pâtissière as per these instructions and keep it to cool down completely.
Cut out strips as long as the sheet of puff pastry (or about 30 cm) and about 2.5 cm – 1 inch wide.
Roll each strip of dough around a cannolo tube (I did 2 strips per cannolo tube, to save some time, but you can do 1 per tube if you prefer). Make sure the pastry strip overlaps itself: you don’t want any holes in your final cannoncino, or the cream will escape.
Brush the top side of the rolled pastry strips with some cold water and coat with granulated sugar.
Put them on a baking tray lined with baking paper, sugar side up.
Bake in a pre-heated oven at 200°C – 390°F for 10-15 minutes, or until golden brown and the sugar has melted.
When ready, carefully remove them form the cannolo tubes (the tubes will be hot, so handle accordingly to avoid getting burnt!) and keep the cannoncini on a wire rack to cool down completely.
When cold, put the Crème Pâtissière in a piping bag and fill the cannoncini with it.
Serve immediately at room temperature.
Fill the cannoncini just before serving, so the shells will remain crunchy.