Ingredients are frugal again, apart from the Gruyère cheese, but no one said leftovers need to be basic did they? So, simply take a couple of slices of bread, remove the crusts and spread with some butter.
Then, spread on some 'made' mustard. I frantically search my fridge for a jar without success, when I remember that I do have some mustard powder, and it's easy to 'make' by adding equal parts of water and mixing. A layer of the gorgeous Gruyère cheese should be cut to fit, and the sandwich cut in two. Fanny reassures me that it should look like a doorstep and not a petite sandwich.
It looks tasty enough to me as is, but Fanny tells me to turn it in beaten egg and roll it in fine breadcrumbs. I've found some very 70's orange ones, yipee!
Next it's simply to fry the coated halves in not very hot oil, giving the cheese time to become soft and gooey and the crumbs golden brown. A fried sandwich seems very unnecessary and Elvis-like, but it's actually quite light and flavoursome, and certainly feels more of a treat than just a boring old cheese sandwich. I am please to make your acquaintance Monsieur Croque. Bonjour.