Season the shrimp with salt and pepper. Using 2 large saute pans, heat the oil until it begins to smoke. Over very high heat, saute the shrimp for 6 to 7 minutes. Transfer to a warm plate, set aside, and keep warm.
To each saute pan, add 1 minced shallot and 1 tablespoon minced tarragon. Saute for 2 to 3 minutes. Deglaze each pan with the sherry and then combine the sauce in one pan. Add the cream and reduce the sauce until it coats the back of a spoon. Whisk in the butter, 1 small piece at a time. Whisk in the mustard, just at the last minute. Do not let the sauce boil, or the mustard will become grainy. Correct seasoning to taste.
Arrange the shrimp decoratively on serving plates, nap with sauce, and sprinkle with chives.