Combine the mashed ube (purple yam), sugar, water, heavy cream, and vanilla extract (if using) in a saucepan. Use an immersion blender or a whisk to blend everything until smooth.
Add the tapioca starch and stir until completely dissolved.
Place the saucepan over medium heat. Simmer the mixture for 8-10 minutes, stirring constantly. It should slightly thicken and coat the back of a spoon.
Remove from the heat and let it cool for about 15 minutes. Pour the mixture into a container and refrigerate for at least 4 hours or until completely chilled.
Once chilled, churn the mixture in an ice cream machine according to the manufacturer's instructions until it reaches a soft-serve consistency.
Transfer the ice cream to a freezer-safe container. Place a piece of plastic wrap directly on the surface, then cover it completely to prevent ice crystals from forming. Freeze for at least 4 hours or until firm in the coldest part of your freezer.
Let it sit at room temperature for a few minutes to soften slightly before scooping. Serve and enjoy!
Notes
Ube (Purple Yam): Use pre-cooked frozen or fresh ube. You can use a smaller amount of your own ube jam and reduce the amount of sugar in the recipe. Purple sweet potatoes like Purple Stokes and Okinawa Sweet Potatoes are excellent substitutes, as they provide similar taste, texture, and appearance. The natural color of ube varies depending on the variety. If you prefer a vibrant purple color, add ube extract to achieve your desired shade.
Tapioca starch: It acts as a stabilizer that thickens the mixture and prevents ice crystals from forming by absorbing excess water. You can use cassava or arrowroot flour in a 1:1 ratio as a substitute. Another option is to use slightly less cornstarch or a small amount of xanthan gum.
Heavy cream: Its higher fat content of at least 36% contributes to a creamy and smooth texture. Full-fat coconut milk or cream can be viable substitutes, while half-and-half may yield a less creamy result.