In a small bowl, whisk the egg yolks then pour a cup of the hot dairy-sugar mixture into the whisked yolks. Continue whisking as you pour.
Pour the egg yolk mixture back into the saucepan and continue whisking . Cook over medium heat, still stirring , until the mixture thickens a tad. If you can dip in a whisker [no - not your mustache] or other metal implement and the mix coats it without running off rapidly - it's sufficient. Don't allow it to boil - only medium heat.
Strain the mixture.
Whisk in the spiced sweet potato puree.
Refrigerate for a few hours until thoroughly chilled.
Process in an ice cream maker as per manufacturers instructions . Transfer to a suitable container, cover, and freeze until firm.
Makes about 1 quart.