How to Make It
In a large pot, cover the dried beans with 3 inches of water. Add the onion, bay leaf and thyme and bring to a boil. Simmer over low heat, stirring occasionally, until the beans are tender, about 1 hour and 15 minutes. Add more water as needed to maintain the water level. Add 2 teaspoons of salt and remove the pot from the heat. Let the beans cool in the cooking water.
In a large pot of salted boiling water, cook the haricots verts until crisp-tender, about 3 minutes. Drain the beans and spread them on a large rimmed baking sheet to cool.
In a small bowl, combine the shallots, garlic, mustard and both vinegars. Add a pinch of salt and let the vinaigrette stand for 10 minutes. Whisk in the olive oil and season with salt and pepper.
Drain the dried beans and discard the onion, bay leaf and thyme. Transfer the beans to a large bowl and add the haricots verts. Add the vinaigrette and toss well. Season with salt and pepper and transfer to a platter. Sprinkle with the parsley and serve.
Although dried beans will last for years, the newer the crop, the more delicious the beans are and the more evenly they cook. So it’s best to buy from a trusted source, like Rancho Gordo, and cook the beans soon after buying.