Mustard is one of the oldest condiments used in French cookery, certainly since medieval days.
Dijon mustard is another of those indispensable food items in France, used with both hot and cold meats, and in salad dressings.
Dijon mustard is made from brown or black mustard seeds - broadly, the husks are removed, the seeds ground, and vinegar is added. Dijon mustard can be made anywhere now - not just in Dijon itself, but even outside of France - but the recipe and method is 'protected' to control new producers and techniques. various aromatic herbs and spices are added to enhance and vary the flavour.
The most famous brands of dijon mustard are Grey-Poupon and Maille.
Although many recipes exist that use a dash of dijon mustard, it is used more commonly with meat dishes as a condiment. The most usual recipe containing Dijon mustard is salad dressing:
Dijon Mustard salad Dressing
10 tablespoons olive oil
3 tablespoons Dijon mustard
3 tablespoons white wine vinegar
large pinch of salt
Balsamic vinegar or lemon juice can be used instead of the white wine vinegar - use only 1-2 tablespoons of these instead of the three for vinegar, and increase the amount of olive oil by a couple of extra spoonfuls.
Put it all in a jam jar, put the lid on, and shake enthusiastically. You might want to put it in a posher container before putting on the table.