Peel gabi and soak in water to prevent discoloration. In a pot over medium heat, place gabi and enough water to cover. Bring to a boil. Cover and cook until fork tender.
Remove gabi from pot and allow to cool. Mash with a fork until smooth. You'll need 3 cups of mashed gabi.
In a wide non-stick pan, combine coconut milk, evaporated milk, condensed milk, mashed gabi, sugar, and butter. Whisk together until well blended.
Bring to a boil, stirring occasionally until sugar is dissolved and butter is melted.
Lower heat and continue to cook, stirring regularly, for about 40 to 50 minutes or until the mixture is smooth, very thick, and can hardly be lifted from the pan.
Brush the bottom and sides of the serving dish with coconut oil.
Transfer the kalamay mixture into the prepared pan, using a lightly oiled knife or spatula to smooth top.
Brush surface with coconut oil and top with latik.