Peel: Peel the yautía with a potato peeler or paring knife, removing the thin brown skin.Chop the yautía and rinse.
Boil: Place the rinsed yautía in a pot, and add sufficient water to cover it plus a couple of inches [5 cm]. Add ¾ tablespoon of the salt to the water.Boil until they are fork-soft. Once boiled remove from the water and discard the water.
Mash: Mash until the mixture is very smooth and there aren't any lumps (a potato ricer or food mill [Amazon affiliate links] is perfect for it).
Mix: Incorportate butter, and then mix in the milk. Incorporate the garlic powder. Taste and season with salt to taste if you find it necessary.