In a bowl fitted into a sauce pan with barely simmering water, whisk the yolks with the lemon juice until light and frothy. Whisk in the butter in 2-tablespoon increments. The sauce will seem thin at first, but continue to whisk until the sauce thickens. Be careful not to overcook because the eggs will scramble. When sauce is thick, remove from heat and stir in remaining ingredients. Serve immediately.