Rognons de Veau à la Moutarde (Veal Kidneys with Mustard)

Sautéed veal kidneys in mustard sauce is one of the most typical old Paris bistro plates. The mustard should give some peppery bite, but the Dijon mustard sold in France is much hotter than the examples exported to the United States (Maille “Extra Hot” made for the United States, for instance, is milder than the standard Maille in France), and anyway mo…