Preparation In a small bowl, whisk together the lemon zest, lemon juice, sugar, mustard, and fine sea salt, whisking until the sugar and salt are dissolved. Add 3 tablespoons of the oil in a slow stream, whisking constantly until the dressing is well blended. Season with fine sea salt and freshly ground black pepper. If desired, whisk in the remaining oil in a slow stream, whisking constantly. DO AHEAD: The vinaigrette can be prepared ahead and refrigerated, in an airtight container, up to 3 days.
Preparation In a small bowl, whisk together the lemon zest, lemon juice, sugar, mustard, and fine sea salt, whisking until the sugar and salt are dissolved. Add 3 tablespoons of the oil in a slow stream, whisking constantly until the dressing is well blended. Season with fine sea salt and freshly ground black pepper. If desired, whisk in the remaining oil in a slow stream, whisking constantly. DO AHEAD: The vinaigrette can be prepared ahead and refrigerated, in an airtight container, up to 3 days.