Combine wine, shallots and tarragon, and cook until wine is reduced to a mere glaze. Combine glaze with egg yolks and salt in blender. Heat butter until bubbling hot. Turn blender on and off once quickly to blend ingredients. Turn on again and gradually pour melted butter in steady stream until sauce thickens. Additional tarragon or parsley may be folded into sauce. Excellent on broiled beef, fish or eggs.