Place the yam in a large saucepan and add enough water to cover it. Bring to a boil over high heat. Cover the pan, lower the heat to medium and continue to cook until fork tender, about 30 to 40 minutes, depending on the sizes of the purple yams. Drain and let stand until cool enough to handle. Peel the yam and then mash with a potato masher or a fork. It will yield 2 ½ cups mashed purple yam. Set aside.

Melt the butter in a pot over medium heat. Add the evaporated milk, coconut milk and condensed milk. Stir and then add the mashed yam. Cook, stirring constantly until very thick and starts to pull away from the side of the pot, about 40 minutes.

Transfer mixture into desired greased containers. Let cool completely.

Top with macapuno strings, if using and serve.