NYT Cooking: A basic vinaigrette deserves a permanent spot in every cook's repertoire. Ready in minutes and fine to keep in the fridge for weeks, it can totally change a salad. And it's highly adaptable. Add garlic or tarragon in place of the mustard, or infuse it with other herbs. For a creamy dressing, replace the oil with buttermilk, crème fraîche or mayonnaise. Some chefs even%...