Step 1 In a small bowl, combine the shallots, lemon juice and vinegar. Set the bowl aside for 5 to 10 minutes to give the shallots time to quickly marinate. Add the salt and pepper, then the olive oil in a slow, steady stream, whisking constantly to combine. Stir in the mustard. Taste for seasoning and add more salt or pepper if desired. This makes about two-thirds cup vinagrette, which can be refrigerated in an airtight container up to 3 days. Bring the vinaigrette to room temperature and whisk to recombine the ingredients before using.