Roasted Fingerling Potatoes with Tarragon-Shallot Butter

lbs fingerling potatoes (mixture of yellow, red, and blue, if possible!)

extra virgin olive oil

freshly ground black pepper

sea salt

unsalted butter

large shallot, finely diced

½ teaspoon whole black peppercorns, coarsely chopped

freshly grated lemon zest

large sprigs of fresh tarragon, leaves removed and finely chopped (plus 1 additional sprig for garnishing)

juice of half a lemon

sea salt