Preheat the oven to 190 degrees Celsius.
Make a paper pattern so all of the puff pastry pieces come out the same size. Cut a triangle with a 10-centimeter base and with a height of 26 centimeters. Measure the height from the center of the base. Using this pattern also helps make best use of the puff pastry and not have a lot of little pieces left over.
Cut the puff pastry using the paper pattern for help and place a slice of ham and cheese on top. In the middle of the base of the puff pastry, cut out a small triangle. This will help when rolling the croissant. Start by rolling from the wide end towards the skinny end very carefully. Finish by curving the pastry into the well-known croissant half-moon shape. Place the croissants on a baking tray lined with parchment paper.
Coat the tops of the pastry with beaten egg so they come out shiny. Bake 15 to 17 minutes until puffed and golden.