The first time I saw a mustard field in full bloom was from the window of a car during a family vacation in France. It was an extraordinary sight; mustard flowers are a stunningly bright shade of yellow, and to see them blanketing the landscape beneath a vibrant blue sky is to feel for a moment as though you're on the surface of the sun.
That may explain my feeling that mustard should always be hot, and why the spicier French and English mustards have a bigger place in my pantry than the sweet bright American version. English mustard claims the crown when it comes to serious heat, but hot, creamy French-style Dijon mustard has the most versatility.
Dijon mustard is a vital ingredient in just about every sandwich I make. It's perfect with eggs or potatoes (i.e.: devilled eggs, egg salad, mashed potato, potato salad), and provides the right finishing note for simple cheese dishes like mac and cheese, raclette, or a grilled cheese sandwich. Add it to hot dishes at the end, not the start, to retain the spiciness on the palette.
Dijon and melted butter make a delicious simple sauce for fish or roasted vegetables (you can use lemon juice for acidity and flour to thicken), and Dijon is essential to one of the simplest and best vinaigrettes you can hope to make.
The use of mustard in food goes back to ancient times. It was known to the Egyptians three millennia ago, it appears in the Bible as part of Hebrew cuisine, and it was used by every Mediterranean civilization up through the Greeks and the Romans.
As anyone who's eaten mustard greens surely recognizes, mustard is part of the brassica family of plants, which also gave the world cabbage, collard greens, and cauliflower. Yet it's the seeds rather than the leaves that are most celebrated for their culinary use. The Romans have the earliest recorded recipes for prepared mustard. Pliny the Elder wrote in his Natural History about mixing ground mustard seed with vinegar, though he used it to treat scorpion stings rather than to flavor a ham sandwich.
The Romans used mustard as both a prepared sauce and as freshly crushed seasoning, like pepper, and the word "mustard" may come from the Roman "mustum ardens." which broadly translates as "spicy grape juice." The Romans brought mustard to every corner of their empire, but it was in Gaul that it really took hold. Mustard became a foundation stone of French cuisine and a favorite of such worthies as Charlemagne, Louis XIV, and Pope John XXII of Avignon. It's no surprise that a former Roman trading post, Dijon, came to establish itself as a commercial mustard powerhouse.
What sets Dijon mustard apart? Originally it was verjuice, the sour juice of unripe grapes, which Dijon-based mustard maker Jean Naigeon used in place of vinegar for a smoother product. Yet the term Dijon mustard is not one of Europe's many protected designations, meaning there are no rules about how or where the product is made. Dijon mustards tend to follow the same style, but the majority are now made outside Dijon, and it's near impossible today to find any made with verjuice.
The closest thing to real Dijon that you'll find on supermarket shelves may be Grey Poupon, not coincidentally judged the best classic Dijon in a Serious Eats taste test. Grey Poupon proudly boasts right there on the label that it's made with white wine, and that combination of white wine and vinegar is as close as you're likely to get to the flavor of verjuice. There is nothing called "poupon" in Grey Poupon, nor does the name represent its pale color; Messrs Grey and Poupon were actually the founders of the brand. Maurice Grey developed new technology for milling and separating mustard seeds in the mid 19th century, and Auguste Poupon bankrolled the operation. Both were based in Dijon, but the product is now made in New York by Kraft and largely unknown in France.
Because there is no regulation about what makes a mustard Dijon, I advise paying attention to the labels to make sure what you're buying will have a flavor and consistency that cuts the mustard, so to speak. Dijon should not be the bright yellow of the mustard crop, but a more modest creamy shade. The impact is all in the flavor, which is hot, strong and complex.
Look for Dijon mustard with the least number of ingredients. Only water, mustard seeds and vinegar are necessary; wine is welcome. Additional acids and sulfites are just about impossible to avoid, though mustard doesn't need a lot of preservatives. As no less an authority than French's will attest, there are no ingredients in mustard that spoil. The product can be safely stored at room temperature, away from heat and light, but the flavor and color may hold up best in the refrigerator.
Many brands include turmeric, paprika or garlic, so be aware of those differences when deciding which brand you prefer. Even Grey Poupon lists mysterious "spices" among its ingredients.
Mustard in a squeezy bottle may contain additional thickeners to change the consistency, though I'm at a loss to why anyone would want to serve Dijon mustard in a squeezy bottle. One doesn't generally trail thick snakes of it across a hot dog. Indeed, if you're used to American mustard, be very careful not to use Dijon interchangeably. Though Dijon is not traditionally the absolutely hottest mustard, the intensity of its flavor may come as an eye-watering surprise!