Prepare 5 dl (18 fl oz or 2¼ U.S. cups) of sugar to 28° on the saccharometer and infuse in it the required flavouring such as vanilla, lemon zest, flower petals etc. If using a liqueur this should be added when the syrup is just lukewarm using ½ dl (2 fl oz or ¼ U.S. cup) of liqueur. It is, however, preferable to use an essence for the flavouring.
Whisk the flavoured or unflavoured syrup slowly on to 12 whisked egg yolks, place over a low heat and cook in the same manner as Crème à l’Anglaise until it thickens. Pass through a fine strainer and whisk in 450 g (1 lb) good quality butter.