Combine the egg yolks and sugar in a mixing bowl. Whip until light and fluffy. Bring the half and half to the scalding point with the vanilla bean, if used. Gradually pour the hot cream into the yolk mixture while stirring rapidly.
Place the mixture over simmering water and heat slowly, stirring constantly, until it is thick enough to coat the back of a spoon. Be very careful not to get it hotter than 190 degrees or it will curdle.
Immediately pour the custard into another container and continue stirring for a minute or so. Remove the vanilla bean and save for another use, or stir in the vanilla extract. Set the sauce aside to cool, stirring from time to time until cold.
Place lemon curd in a medium mixing bowl and whisk in 3 tablespoons of creme anglaise, until a smooth consistency has been achieved. Fold in remaining creme anglaise. Store covered and refrigerated. The sauce will keep for about 3 days.