Combine milk, cinnamon stick, nutmeg and vanilla in a heavy saucepan over medium-low heat.

Bring the mixture to a very gentle boil.

Meanwhile, in a large bowl, whisk egg yolks with the sweet potatoes, sweet potato syrup and sugar until very well combined and no chunks remain.

Remove cinnamon stick from milk mixture (discard) and slowly pour hot milk into egg yolks to temper yolks.

Return mixture into saucepan and cook over medium heat (do not allow to boil) until mixture thickens and reaches a temperature of 160 degrees F. (mixture should be thick enough to coat the back of a wooden spoon).

Remove from heat and stir in cream.

Transfer to a sterilized glass jar and refrigerate for a minimum of 4 hours until well chilled. Serve with whipped cream and a sprinkling of pumpkin pie spice, if desired.

Serve with a dollop of whipped cream and a sprinkling of pumpkin pie spice, if desired.