1. Start by opening your croissants in half using a knife without completely separating them.
2. Preparation of the béchamel sauce:
3. Melt the butter in a saucepan, add flour and gradually whisk in milk (quantities to your taste) while stirring. Let it thicken over low heat, stirring constantly. Add salt, pepper, and nutmeg.
4. As soon as your béchamel sauce is ready, melt cheese in it and spread it inside the croissants. Add a rolled slice of ham, then more béchamel sauce and grated cheese.
5. Repeat this for the other 3 croissants.
6. Place in the oven at 180°C (350°F) for 20 minutes, while keeping an eye on them.