I can’t tell from the instructions if the Croque Monsieur sandwiches use one (open face) or two slices of bread (top and bottom).
The sandwiches are double sided (made with 2 slices of bread) and not open sandwiches. So each sandwich contains two slices of cheese and one of ham. We would suggest putting each slice of ham in between two slices of cheese before encasing in the bread. The top bread slice of the sandwiches should also crisp up slightly in the oven as the dish bakes.