Dish · french
Croque Monsieur
Grilled ham and gruyere sandwich coated in béchamel sauce, then baked or broiled until the top browns and the cheese inside melts.

Where it comes from
Paris cafes served it as a fast lunch by the early 1900s, named for the crisp crust rather than any documented origin story. A fried egg on top turns it into a croque madame.
What cooks argue about
Cooks argue over whether béchamel belongs inside the sandwich, on top, or both, and whether the bread gets dipped in the sauce or the sauce ladled on separately.
Versions
Nobody has published a croque monsieur here yet. When somebody cooks one from a video and publishes it, their version appears in this list, with a link back to the original.
What goes in it
Each one opens everything else made with it.