Put vinegar, mustard, tarragon, egg yolks, salt and pepper in a mixing bowl and whisk briskly until smooth. Put oil in a measuring cup with a pouring lip. While continuing to whisk mixture, slowly add oil in thin, steady stream. As mixture thickens, increase the flow of oil until all oil is used. Store in air tight container in refrigerator. Can be stored for several days.
Recipe courtesy of The Butcher Shoppe.