1 cup extra-virgin olive oil
1/2 cup balsamic vinegar
1-1/2 teaspoons kosher salt
1 garlic clove, minced
1/4 teaspoon sugar
1/4 teaspoon freshly ground pepper
1-1/2 pounds assorted heirloom tomatoes (found in most specialty produce markets) or, if heirloom tomatoes are not available, cherry, vine-ripened, or grape tomatoes
4 large fresh basil leaves, julienne cut
Garnish: whole basil leaves
3 days ahead: Make dressing: Whisk together olive oil and next five ingredients.
2 hours ahead: Cut smaller tomatoes in half; quarter larger tomatoes. Set aside. Drizzle dressing over tomatoes. Sprinkle with basil. Let stand at least 15 minutes and up to 1 hour.
Just before serving: Drain excess liquid. Garnish with fresh basil leaves; serve at room temperature.