Peel the taro and ube with a peeler. Cut them into small pieces for easier cooking.
Place the chopped taro and ube into two separate bowls and steam for 10-20 minutes, or until a fork can easily poke through.
Mash the taro and ube using a fork. Add sugar (optional for a hint of sweetness in the purée). Set aside until cool.
In a food processor, blend 100g taro, 5g sugar, and 35g milk until smooth and lump-free. Transfer to a ramekin or container to create a pure taro purée.
Without washing the food processor, blend 85g taro, 15g ube, 5g sugar, and 35g milk until smooth and lump-free. Transfer to a ramekin or container to create a light-purple taro purée.
Again, without washing the food processor, blend 70g taro, 30g ube, 5g sugar, and 35g milk until smooth and lump-free. Transfer to a ramekin or container to create a purple taro purée.
Finally, without washing the food processor, blend 45g taro, 55g ube, 5g sugar, and 37g milk until smooth and lump-free. Transfer to a ramekin or container to create a dark-purple taro purée.
The purée is now ready to serve. You can use it as a spread on toast or add milk to make a drink.