1: Begin by cutting the crusts off 12 slices Sandwich bread.
2: Cut 3 slices ham to the size of the bread slices.
3: Lightly fry the slices of ham in a very hot pan for just a few seconds on each side.
4: Spread béchamel sauce on 2 slices of bread (tip: use a broad-bladed knife or palette knife). Place a piece of ham on top of the sauce on one slice of bread.
5: Then put the other slice of bread on the ham and sprinkle with grated cheese.
6: Place the croque-monsieur on a baking sheet. Preheat the oven to 200°C (390°F).
7: If you are making several croque-monsieurs, it is worth setting up a production line, i.e. spread béchamel sauce on all the bread, then arrange all the slices of ham, etc. This is much faster than doing one at a time.
8: Once all your croque-monsieurs are assembled, put the baking sheet into a hot oven.
9: Cook for about twenty minutes, watching carefully for colouring. You can put them under the grill to brown if necessary at the end.
10: Serve hot or warm if possible, with a green salad for example.
Remarks
You can use whatever ham you prefer; I find that it's best with smoked ham, but it's a matter of taste. The same goes for the cheese. Gruyère, or even better Comté, will give you the best croque-monsieur. yYu can cut the left-over crusts into small pieces and fry them in a little clarified butter or oil, to make small croutons which are great for adding to salads, for example.