Following the directions in sauce parisienne, cook the butter and flour slowly together for 2 minutes. Off heat, blend in the boiling cooking liquid, then the milk. Boil 1 minute. Blend the egg yolks and cream in a bowl, then beat the hot sauce into them by driblets. Return the sauce to the pan and boil, stirring, for 1 minute. Thin out with more cream if necessary. Season to taste with salt, pepper, and lemon juice. Strain.