In top of double boiler, combine 1 tablespoon butter, arrowroot, milk, salt, and egg yolks. Stir with wire whip until well mixed. Place top over boiling water and whip until mixture thickens. Remove top of double boiler and gradually add remaining butter cut into small pieces, whipping constantly, until smooth and well blended. Correct seasoning. Add lemon juice and pepper.
Good with white-meated fish or boiled vegetables.