The Croque-Mademoiselle is the lighter sister of the Croque-Monsieur, a deliberate scaling-back of the format for diners who want the silhouette of the sandwich without its full architectural weight. The build varies by kitchen, but the through-line is restraint. Some versions skip the béchamel entirely and let melted Gruyère do the binding alone. Others keep a thin béchamel but cut the cheese in half. A few use a leaner ham, less butter on the bread, or pain de mie sliced thinner than the classique would call for. The result is a sandwich that reads as a croque on the menu and arrives as something noticeably gentler on the plate. The name plays on the diminutive of madame: smaller, younger, less imposing. Whether the kitchen interprets that as a calorie cut, a portion cut, or a richness cut depends on the café.
The variant rewards a particular kind of weekday eater. A standard croque-monsieur is a substantial lunch, the kind of dish that buys an afternoon of focus and a four-pm coffee. The Mademoiselle is a midday sandwich that does not interrupt the afternoon. It is also the format that lets a kitchen serve the croque to diners who want the experience but cannot, or will not, eat the full version. A salad on the side is standard. A glass of something dry rather than something rich is the matching drink. The bread still has to be good, the ham still has to be jambon de Paris, the cheese still has to actually melt. The reduction targets richness, not quality. A poorly-made Mademoiselle is just a thin ham-and-cheese sandwich on bread that is not pulling its weight.
The Mademoiselle is not a strictly codified recipe in the way the Madame is, which is part of why it appears on some menus and not others. It belongs to the same impulse that produced lighter versions of richer dishes across French café cuisine, an attempt to bring the sandwich's basic pleasure inside a leaner envelope. The full cluster of croque variants is mapped at Croque-Monsieur. The Mademoiselle is the version for diners who want the format without committing to the broiler-and-béchamel maximalism it can reach at its peak.