If you think about it, the cousin of the Croque-monsieur, the Monte Cristo, is sort of over the top. The bread is typically French toast, and it's filled with ham, (with the common addition of turkey), along with Swiss cheese. Delish Diner's Monte Cristo ($8.50) uses challah bread for their French toast, which is sweet and rich by default. The egg batter for the bread is also sweet, with a good hit of cinnamon. Its exterior is somewhat oily (I ended up having to use a few napkins), and if you're dainty you might want to use a knife and fork.
The first bite of piping hot sweet French toast, ham, turkey, and melted cheese is richly satisfying, but after a few more bites, the whole thing starts staggering over its own heaviness. The ham and turkey aren't particularly flavorful, which is a shame because the salt in both helps cut through the French toast in a good Monte Cristo, so the balance of flavor falls mainly towards the sweet side. It is a monster of a sandwich, so don't feel bad if you can only eat half of it. Share it with a friend, your mother, or a very hungry small child, even, because sharing is caring.