Cook the beans in a large pot of boiling water with a good tablespoon of salt until tender crisp (4 to 5 minutes; best to check at 4 minutes!). Drain, rinse with cold water and immerse in an ice water bath to stop the cooking process. I put the colander into a very large bowl of ice water for this, so I don’t have to pick ice cubes out of the beans. As soon as they're cooled through, drain thoroughly and pat them dry (rolling them in a tea towel works well, too). (If you don’t plan to use them right away, you can dry them, wrap them in a tea towel, seal in a container and store in the refrigerator for up to one day.)

Combine the oil and vinegar (plus sugar, if using) in the bottom of a large serving bowl, and toss in the shallots and basil. Whisk well with a fork and add the tomatoes as you halve them. Grind in pepper to taste, stir again and then add the beans. Toss everything together until all the beans are coated with the dressing and the tomatoes, basil and shallots are happily intermingled among the beans. Serve right away, or cover and chill for at least an hour and up to 4 hours, tossing occasionally. Serve the salad cold or at room temperature.