This ingredient is to the French what ketchup is to us: the go-to condiment — it comes to the table at every café along with the salt and pepper. The best-known mustard is named for the Burgundian city of Dijon (actually, Dijon mustard refers to a style of mustard, one that’s smooth, sharp, and strong), but mustard didn’t originate in France: it appears to have arrived with the ancient Romans. The fact that the French didn’t invent mustard didn’t stop them from adopting it and manufacturing their own, and by medieval times, it was a kitchen staple. Pope John XXII, living in Avignon in the fourteenth century, established the position of “Pope’s First Mustard Maker,” and two centuries later, the Sun King, Louis XIV, took to traveling with his own mustard pot in tow. In fact, mustard pots are still traditional wedding presents in France, and you can still bring your own little pot to shops like Maille for a refill. The two mustards that I keep on hand at all times and used in these recipes are Dijon and grainy, known as moutarde à l’anciènne, or old-fashioned mustard, but if you’re a mustard lover, I urge you to experiment. Mustard with green peppercorns makes a wonderful addition to vinaigrettes and horseradish mustard is great with steak . . . and frites.