Heirloom Tomato Salad with Mozzarella and Basil

INGREDIENTS

• 1/2 cup extra-virgin olive oil
• 4 lb mixed heirloom tomatoes, quartered if small or cut into 1/4-inch-wide wedges if larger
• 2 tablespoons red-wine vinegar
• 1/2 teaspoon sugar
• 1 1/2 cups loosely packed small basil leaves or torn large leaves
• 1 teaspoon salt
• 1 lb cherry tomatoes
• 1 lb very small mozzarella balls (1/4 inch; sometimes called perlini) or 1 lb lightly salted mozzarella, cut into 1/4-inch pieces
• 1 teaspoon Dijon mustard
• 1/2 teaspoon black pepper