Preparation Whisk together vinegar, mustard, salt, sugar, and pepper in a large bowl. Add oil in a slow stream, whisking constantly until dressing is emulsified. Add tomatoes, mozzarella, and basil and toss well. Season with salt and pepper. Cooks' notes:•Salad, without vinaigrette, can be assembled 2 hours ahead and kept at room temperature. Salad can be dressed 1 hour ahead and kept at room temperature, covered. •Vinaigrette keeps, covered and chilled, 1 week.
Preparation Whisk together vinegar, mustard, salt, sugar, and pepper in a large bowl. Add oil in a slow stream, whisking constantly until dressing is emulsified. Add tomatoes, mozzarella, and basil and toss well. Season with salt and pepper. Cooks' notes:•Salad, without vinaigrette, can be assembled 2 hours ahead and kept at room temperature. Salad can be dressed 1 hour ahead and kept at room temperature, covered. •Vinaigrette keeps, covered and chilled, 1 week.