Turn the oven to 325 F degrees.
Boil 3-4 cups of water in a kettle, set it aside.
In a medium bowl, mix eggs.
In a small saucepan, combine pureed sweet potato, cream, milk, 1/4 cup of sugar, and vanilla extract. Heat the cream mixture until sugar is dissolved and hot, but not boiling.
Tempering: pour a small amount of cream mixture to the egg mixture, mix well, then add more cream mixture until all are well incorporated. (Note: never pour all hot liquid once into the egg mixture as they solidify.)
Using a fine mesh or a sieve, strain 5). Discard any lumps from eggs.
Pour 6) into individual ramekins.
Place the ramekins in a baking dish then pour enough hot water from the kettle into the pan to come halfway up the sides of ramekins.
Place a cover and bake until creme brulees are set, about 25-35 minutes (Note: the time might vary depending on a type of oven using and how hot the water is).
Remove creme brulee from the oven and let them cool. Remove ramekins from water and place them in the refrigerator to cool thoroughly.
To serve, sprinkle about one teaspoon of a creme brulee and spread them equally. Using a torch, melt the sugar to form a crispy top. Let the sugar settle before serving, about 1-2 minutes.