Preheat your oven to 350° Fahrenheit/ 180° Celsius.
Cut open your croissant lengthwise, just enough to create a pocket.
Wrap your ham around the cheese if it's a large slice of ham or just place 1 slice of ham over a one slice of cheese.
Fill the croissant with the ham and cheese. Try to stuff it if the ham and cheese are looking out of the croissant.
Place a baking sheet over the baking tray.
Place your stuffed croissant on the baking sheet and bake your croissant at 350° Fahrenheit/ 180° Celsius for about 5 minutes or until you see the cheese melting.
Take out the hot croissant sandwich and leave to cool a bit. Enjoy still warm with the cheese melting out.