This is going to be the fanciest ham and cheese sandwich you will ever have. Leave it to the French to take something so simple and humble and top it with tons of cheese and toast it until golden brown. And to top it off, let’s put a fried egg on it. Typically made on basic white bread, I’ve taken this dish even further and made it on a croissant. There’s one thing that will happen after having this: you’ll never be able to go back to a regular ham and cheese sandwich.
Spread the bechamel to the edges of the croissant to prevent the edges from burning.
Heat the butter over medium-low heat in a medium sized saucepot. Once the butter is completely melted and begins to bubble, add the flour and whisk until combined. Switch to a heat-proof rubber spatula and continue stirring until the mixture is a light golden colour and smells slightly nutty. Be sure to scrape all around the sides and bottom to ensure nothing is sticking or burning.
Whisking constantly, slowly pour the milk into the pot. Switch back to the rubber spatula and cook, constantly stirring and scraping the sides and bottom, until thick and bubbly. About 8 minutes.
Turn the heat off and stir in the salt, black pepper, nutmeg, Gruyere and Parmesan until cheese has melted. Set aside to cool.
Pre-heat the oven to broil and set the rack in the middle of the oven. Slice the croissants open and spread a generous amount of mustard on each half. Lay the ham on the top halves of the croissants and top with the bottom halves. This will give the bechamel a nice flat surface to sit on. Transfer the sandwiches onto a sheet pan.
Top each sandwich with lots of bechamel spreading it to the edges of the croissant. This will prevent the edges of the croissant from burning in the oven. Combine the Gruyere and Parmesan and top each sandwich with the cheese. Season with salt and pepper.
Place sandwiches under broiler for about 2 minutes, rotating pan halfway through, until cheese and bechamel are melted and bubbly.
Remove from the oven, plate each sandwich with a fried egg, garnish with chopped chives, fresh black pepper and Maldon salt.