In a small saucepan bring the cream, ginger and lemon zest just to a boil. Remove pan from heat and let mixture stand, covered, 15 minutes
In a bowl with an electric mixer beat yolks with sugar until mixture is thick and pale
Whisk the yolk into the cream and heat over moderately low heat, whisking, until a candy thermometer registers 160°F. Remove the pan from the heat. Strain sauce through a sieve. Discard the lemon zest and the ginger.
