To quick-pickle the shallots, combine them with the vinegar in a small bowl and set them aside to soak for a few minutes.
1/2 cup shallot, 2 tablespoons white wine vinegar
Add the potatoes and 2 teaspoons of salt to a large saucepan, then cover them with 10 cups of cold water. Bring to a boil over medium-high heat, then lower the heat to medium. Let the potatoes cook, undisturbed, until they are fork-tender, about 12 to 15 minutes. Drain the potatoes and transfer them to a large bowl.
24 ounces baby Yukon Gold potatoes, 2 1/2 teaspoons Kosher salt
Using a slotted spoon, carefully lift the shallots out of the vinegar and add them to the bowl with the potatoes. Set the vinegar aside in the small bowl for later use. Leave the potatoes intact, or for more texture in the finished salad, use a potato masher to mash about 1/3 of the potatoes right in the bowl.
To the reserved white wine vinegar, add lemon juice, Dijon mustard, pepper, and the remaining ½ teaspoon of salt. Whisk until well combined, then slowly whisk in the oil until the dressing is smooth and emulsified.
2 1/2 teaspoons Kosher salt, 1 tablespoon lemon juice, 1 teaspoon Dijon mustard, 1/4 teaspoon black pepper, 2 tablespoons olive oil
Pour the lemon-vinegar dressing over the potatoes, then add the celery and tarragon. Gently toss everything together to coat. Serve right away, or cover and refrigerate for up to 12 hours. Before serving, garnish with extra tarragon leaves for a fresh touch.
1 stalk celery, 1 tablespoon tarragon