Preheat the oven to 200 degrees Celsius / 392 Fahrenheit with top and bottom heat.

We start by making the béchamel sauce. Melt the butter in a heavy-bottomed saucepan.

Once the butter has melted, add the flour and cook it briefly. Then add the milk and whisk it well with a whisk. Cook it down until you have a nice thick, creamy sauce (the consistency of thick custard).

Then add the mustard, parsley, pepper, and salt to taste and set it aside.

Now we’re going to assemble the croque monsieur. Place two slices of bread on a baking sheet lined with parchment paper. Spread some of the béchamel sauce over the two slices of bread.

Place the ham on top, then half of the grated cheese, another slice of bread, and finish it with the remaining béchamel sauce and grated cheese.

Put the croque monsieur in the oven for about 10–15 minutes until the cheese is melted and golden brown. Enjoy your meal!