Step 1 Place the wine, vinegar, tarragon, shallots, pepper and sugar in a small saucepan. Bring to a boil. Cook rapidly over high heat until almost all the liquid has evaporated, about 3 to 5 minutes.
Step 2 Heat the butter in another small saucepan until bubbly, but not browned.
Step 3Place the egg yolks, lemon juice, salt, white pepper and mustard in a blender container. Blend on low speed about 5 seconds.
Step 4With the blender running, add half the butter in a slow, steady stream until the blender blades are covered. Then increase the speed to high and slowly add the remaining butter and cooked wine mixture.