Shake can of coconut milk well. Pour coconut milk into a 1-quart measure. Add whole milk to make 3 cups. Pour milk into a saucepan and add tapioca, sugar and egg. Stir gently just to combine, then let set 5 minutes.
Over medium heat, bring tapioca mixture slowly to a full boil, stirring constantly with a rubber or wooden spatula. At the boil, remove from heat. Fold in fruit of choice. Pour into ramekins, dessert bowls, or lidded containers. Cool 20 minutes.
Stir tapioca well in each container, then chill. Tapioca will thicken as it cools.