Prepare a large bowl filled water and ice. Set aside. Fill a large pot of salted water and bring to a boil over high heat. Add carrots to water and cook for 4 - 5 minutes. Drain the carrots in a colander, then plunge them into the bowl of ice water. Allow carrots to cool slightly. Drain again in the colander, pat dry with a towel and set aside. In a large skillet over medium-high heat, add olive oil and butter. Add shallot and cook until softened. Add carrots, tarragon salt, and pepper. Sauté carrots until thoroughly heated. Serve immediately.