Peel and slice the yams into inch thick slices. Transfer into a medium pan, rinse, then cover with cool water. Bring to boil and simmer until tender. Mash with a fork.
Crack eggs into a large bowl. Beat with a whisk until yellows and whites are combined.
Gradually add sugar and whisk until combined.
Add oil and whisk until combined. Add chopped macapuno and vanilla and stir with a wooden spoon to combine.
Sift together flour, baking powder, baking soda, and salt in another bowl.
Add about a third of the flour mixture to the wet mixture and mix to combine.
Add about one half of the buttermilk and mix to combined.
Repeat above, alternating flour and buttermilk and ending with the flour mixture.
Scoop into cupcake papers about half to two-thirds full (depending on whether you want flat or domed cupcakes. Note that these cupcakes will don't shrink. Two-thirds full will result in domed cupcakes.).
Bake for 22-25 minutes until a cake tester comes out clean.