Mix up a classic croque monsieur with different cheeses and, in an autumnal twist, a rich leek and bechamel base

While I love a classic croque monsieur (or madame), I do occasionally like to mix things up by using different cheeses and hits of other condiments – I basically live life on the edge. This leek-laced version feels comfortingly autumnal, and a bit special, too. If I have friends coming over, I’ll make the leek and bechamel base in advance, then fill the sandwiches just before baking and serve them with a bitter leaf salad.