How to Make It
In a small bowl, whisk the sherry vinegar with the shallot and Dijon mustard. In a thin, steady stream, whisk in the olive oil until emulsified. Season with salt and pepper.
Herb Vinaigrette Add 1/4 teaspoon chopped thyme and 1/2 teaspoon chopped tarragon.
Lemon Vinaigrette Substitute 1 1/2 tablespoons lemon juice for the vinegar and add 1/4 teaspoon grated lemon zest.