Summer vegetable potato salad

11⁄2 pounds small waxy potatoes, left whole or cut into large bite-sized chunks;

3 tablespoons dry white wine;

3 tablespoons white wine vinegar or rice vinegar;

8 ounces slender green fillet beans and/or yellow wax beans, ends trimmed;

1 tablespoon wholegrain Dijon mustard;

2 teaspoons kosher salt, plus more to taste;

1 teaspoon ground black pepper, plus more to taste;

1⁄2 cup extra-virgin olive oil;

1⁄2 cup thinly sliced red onion;

1 cup whole miniature tomatoes, as many colors as possible;

1⁄4 cup chopped flat-leaf parsley;

1⁄4 cup chopped fresh basil.

Place the potatoes in a large pot and cover with cold water. Bring to a boil, add 1⁄2 teaspoon kosher salt per cup of water, reduce the heat, and cook at a low boil only until the potatoes are tender when pierced with the tip of a knife, about 15 minutes. Do not overcook them or they will start to fall apart and get waterlogged. Drain them in a colander and return them to the hot pot to let any remaining moisture evaporate away. Spread the hot potatoes in a single layer on a rimmed baking sheet, sprinkle with the wine and vinegar, and let cool to room temperature. The potatoes will absorb most of the liquid as they cool. Transfer the cooled potatoes and any standing liquid into a large bowl.
Fill a large bowl with ice water. Bring a medium saucepan of water to a boil. Add 1⁄2 teaspoon kosher salt per cup of water. Add the beans and cook until barely tender, 5 to 8 minutes, depending on their size. Transfer with a slotted spoon into the ice water to stop the cooking and set the color. Drain well, pat dry, and set aside.
Whisk together the mustard, salt, pepper, and oil in a medium bowl. Pour over the potatoes and stir gently until the potatoes are coated. Stir in the beans, onion, and tomatoes. If the salad seems dry, drizzle in a little more oil. Season with additional salt and pepper. Just before serving, stir in the parsley and basil. Serve at room temperature.