Thickening or Enriching

To thicken a preparation (usually a sauce), add either egg yolk, butter, beurre manié, flour, or other starch to give it more consistency.

If you are using egg yolks to thicken a hot liquid, begin by pouring a little of the hot liquid into the yolks and mixing well. This will heat the yolks somewhat and prevent them from coagulating when they come into contact with the hot substance.

Butter should be unsalted and well chilled: dice it and whisk it in gradually until you have the right consistency; do not allow it to boil for any more than a couple of seconds, otherwise the butter will separate.