Combine whole eggs, yolks, milk and sugar in a double boiler, stirring continously. When the mixture becomes syrupy and well blended, add the potato and vanilla extract, mixing well, until mixture holds together and starts to separate from the pan. Cool, and refrigerate for 1 hour for easier handling.

To make the caramel coating, combine the sugar, water and cream of tartar in a saucepan, and heat over medium heat. Continue stirring until the syrup turns golden brown (caramel) about 8-10 minutes. Keep it warm over a very low heat.