Preparation In a small bowl, whisk together the shallots, vinegar, and 1/4 teaspoon fine sea salt; let the mixture stand 10 minutes. Whisk in the mustard, then add the oil in a very slow, thin, steady stream, whisking constantly until the dressing is emulsified. Season with fine sea salt and freshly ground black pepper. DO AHEAD: The vinaigrette can be prepared ahead and refrigerated, in an airtight container, up to 1 week.
Preparation In a small bowl, whisk together the shallots, vinegar, and 1/4 teaspoon fine sea salt; let the mixture stand 10 minutes. Whisk in the mustard, then add the oil in a very slow, thin, steady stream, whisking constantly until the dressing is emulsified. Season with fine sea salt and freshly ground black pepper. DO AHEAD: The vinaigrette can be prepared ahead and refrigerated, in an airtight container, up to 1 week.