Cover the potatoes with water in a pot and bring to a boil. Simmer for 15 - 30 minutes, until tender when pierced with a fork. Place in a colander to drain, and cover with a towel to steam for 10 minutes. When the potatoes are just cool enough to handle, peel and cut into 1/2 inch chunks. Place the potatoes in a mixing bowl.
While cooking the potatoes, combine the mayonnaise, lemon juice, vinegar, 2 teaspoons salt, and the pepper. Combine the dressing with the warm potatoes and mix well. Add the scallions, red onion, tarragon, and dill and mix to combine.
Allow the salad to sit for at least 30 minutes before serving so the flavors can blend. Garnish with a bit of tarragon and dill and serve at room temperature.