The French masculine noun croque-monsieur designates a sandwich filled with ham and cheese, and toasted or grilled.

It is composed of:
– croque, conjugated form of the verb croquer, to bite, to crunch,
and
– the noun monsieur (the reason that this noun was chosen is unknown).
—Cf. also ‘croque-madame’: meanings and origin.

Surprisingly, although the croque-monsieur has long been a popular bar snack in France, it seems to have originally been an upper-class item of food. At least that is what the texts in which the noun croque-monsieur first occurs seem to indicate.

The first of these texts is En Wherry. Trois semaines dans les Broads du Norfolk, a novel published in instalments, from 25^th August to 25^th December 1891, in La Revue Athlétique (Paris: Librairie Ch. Delagrave). In this novel, three French persons, nicknamed la Timonnerie, le Diplomate and le Capitaine, spend three weeks cruising the Norfolk Broads aboard a wherry. La Timonnerie is the wife of le Diplomate, who is employed in the French diplomatic service; le Capitaine is so nicknamed because he is a keen sailor and owns a yacht.

The chapter in which croque-monsieur occurs was published on 25^th September 1891:

Il est tard et nous avons grand faim. Que faire pour le déjeuner ? Le jambon devient monotone à la longue. Le Diplomate qui est un peu gourmand, en quoi il ressemble à Talleyrand, a une idée. « Faisons des croque-monsieur ». Vite le pain à toast, le beurre, le fromage de gruyère, le jambon, un peu de poivre de Cayenne et à l’œuvre. L’un coupe, l’autre beurre, le troisième réunit le tout en sandwichs que Vincent fait sauter dans la poêle.
Ils sont exquis, les croque-monsieur.
     translation:
It is late and we are very hungry. What to make for lunch? Ham becomes monotonous in the long run. Le Diplomate who is rather fond of food, in which he resembles Talleyrand, has an idea. “Let’s make croque-monsieurs”. Quick the bread, the butter, the Gruyère cheese, the ham, a little Cayenne pepper and down to work. One cuts, the other butters, the third puts the whole together into sandwiches which Vincent fries in the pan.
They are delicious, those croque-monsieurs.

The second-earliest text in which the noun croque-monsieur occurs is an article titled Nos domestiques (Our servants), by Fernand Vandérem, published in Le Journal Quotidien, Littéraire, Artistique et Politique (Paris, France) of 17^th May 1893. The author mentions two of the dishes that are served at “les somptueux dîners”: “les Croque-Monsieur béarnaise” and “le Chaud-froid Loïe-Fuller”.

Perhaps, “les Croque-Monsieur béarnaise” refers to croque-monsieurs served with béarnaise sauce. The noun chaud-froid designates a dish composed of cooked meat, fish, etc., served cold in aspic jelly or sauce. Loïe Fuller (Marie Louise Fuller – 1862-1928) was a U.S. actress and dancer.

The earliest occurrence that I have found of croque-monsieur in an English text is from the column Paris Day by Day, published in The Daily Telegraph (London, England) of 29^th February 1908. The Paris correspondent for this newspaper reprinted the following menu, published in the journal of a cookery school “where modern French girls, who, it seems, are reverting to the housewifery of their grandmothers, learn the great art enthusiastically”:

LUNCH FOR NINETEEN PERSONS.
Pot-au-feu rapide, 1s 10d.
Croque Monsieur, 2s.
Œufs à la Polignac, 4s 4d.
Bœuf bouilli à la crême, 1s 3d.
Barbue Mornay, 4s 2d.
Veau Orloff, 5s 2d.
Purée de Céléri, 1s 9d.
Capucin Salad, 1s 7d.
Biscuits and tea, 11d.
Total for nineteen persons, 23s.

The correspondent then commented:

We have no idea what Croque Monsieur or Orloff veal may be, or why tea comes in at dessert, but it all certainly seems cheap enough.

The noun then occurs in The Belgian Cook-Book (New York: E. P. Dutton and Company, 1915), “a collection of characteristic and original Belgian recipes, collected from Belgian refugees in England”, edited by Mrs. Brian Luck:

Entrée (Croque-monsieur)

Cut out some rounds of crumb of bread, of equal size, with a tin cutter; or, failing that, with a wine-glass. Butter all the rounds and sprinkle them with grated cheese—for preference with Gruyère. On half the number of rounds place a bit of ham cut to the same size. Put a lump of butter the weight of egg into a pan, and fry with the rounds in it, till they become golden. When they are a nice color, place one round dressed with cheese on a round dressed with ham, so as to have the golden bread both above and below. Serve them very hot, and garnished with fried parsley.
[E. Defouck.]