Coconut Rice Bundles with Bananas and Beans (Khao Tom Mat)

I had wanted to make these ever since I saw them in a Thai cookbook two years ago.  They're made from sticky rice cooked in coconut milk, sugar and salt, and then mixed with cooked black beans, wrapped around a quarter of a banana and steamed in banana leaves until soft and gooey.  And then I remembered I don't like cooked bananas (except in banana bread).  The banana turned strangely purple.  These are yummy, though, especially when garnished with some extra coconut cream and a few drops of soy sauce.  If I were to make these again, I would probably leave out the banana or use something without that cloying banana flavor, like a slice of sweet potato or plantain.