Place the potatoes in a large pot and cover with cold water by 1 inch. Stir 2 tablespoons salt into the cooking water. Bring to a boil over high heat, then reduce the heat and simmer for 5 to 10 minutes, or until fork-tender. Drain and allow to cool slightly.

In a medium bowl, whisk together the olive oil, mustard, lemon juice, mayo, vinegar, garlic, salt, and several grinds of pepper.

Transfer the potatoes to a large bowl and pour in the dressing. Stir to coat, then add the celery, scallions, chives, and dill and stir to combine. Cover and refrigerate for at least 1 hour to allow the flavors to meld.

When ready to serve, season the salad to taste, adding more lemon juice, if desired. Garnish with more chives and serve.