Place the potatoes in a large pot and cover with water. Bring to a boil, cover, and cook for about 20 minutes or until potatoes are tender. Drain and cool completely.
While the potatoes cool, combine the lemon zest, lemon juice, vinegar, garlic, dijon, whole grain mustard, honey, and salt in a blender. Blend well, while blending gradually add the olive oil until creamy. Set aside.
Once cold, dice the potatoes and place in a large bowl. Pour the dressing over top and sprinkle with the tarragon. Gently stir.
Allow to set, refrigerated, for at least 30 minutes before serving.
Notes
TIP: To speed the cooling of the potatoes, remove them from the hot water and place them into a bath of cold water and ice.