It’s not the lettuce or tomatoes that determine whether tonight is a salad night, or even the clock that insists the rest of dinner will be ready in ten minutes. You know what it is? It’s the dijon mustard, present and accounted for in the fridge. This mustard. It’s going to become your favorite note in the vinaigrette: spicy, piquant, perfect. Also great in sauces, glazes, marinades and for standing in for the usual yellow stuff in everything from deviled eggs to slaws and, if you’re so inclined, hotdog buns.