Croque-monsieur is one of those simple little treats that have a few variations depending on how much work you wish to put into it.  ‘Authentic’ versions of the sandwich include a white sauce along with the ham and cheese.  Delia Smith’s version does not include a sauce and is grilled (broiled) in the oven.

2 large slices good-quality white bread, buttered
2 oz (50 g) Gruyère, finely grated
2-3 slices smoked cooked ham, Parma ham or wafer-thin ham
½ oz (10 g) butter, melted
1 level dessert spoon finely grated Parmesan (Parmigiano Reggiano)
salt and freshly milled black pepper

Pre-heat your oven to high grill (note that ‘grill’ is British for broil; you may also use a stove-top non-stick pan or a Panini grill to do the job).

This could not be simpler. On one slice of the buttered bread, spread half the grated Gruyère, then cover that with the slices of ham, folding them if need be to fit the size of the bread. Now sprinkle the rest of the Gruyère on top of the ham, season, then press the other slice of bread on top of that and press it down very firmly. You can at this stage cut off the crusts, but I think they add extra crunchiness. Now brush half the melted butter on the top side of the sandwich, sprinkle it with half the Parmesan and press it in. Now transfer the sandwich to the grill pan and grill it for about 2 minutes, 2 inches (5 cm) from the heat. When it's golden brown, turn it over, brush the other side with the remaining melted butter, sprinkle the rest of the Parmesan all over and grill for another 2 minutes. Then remove it from the grill, cut it into quarters and eat it while it's still crunchy.

These scrumptious little sandwiches also go very well with all kinds of bubbly.