Wash and dry the banana leaves. Pass briefly over low heat to soften, then cut into sixteen 8×8-inch pieces.
Whisk the plain mixture ingredients in a pan until smooth. Cook over medium-low heat for about 10 minutes, stirring constantly, until very thick and pulling away from the sides. Transfer to a bowl.
Wipe the pan clean. Whisk the chocolate mixture ingredients until smooth. Cook over medium-low heat for about 10 minutes, stirring constantly, until very thick and pulling away from the sides. Transfer to a bowl.
Spread 2 tablespoons plain mixture in the center of each leaf. Spread 1 tablespoon chocolate mixture on top, keeping it within the plain layer. Use the leaf to roll into a log. Wrap snugly without squeezing, then fold in both ends.
Place in a steamer, seam-side down. Bring the water to a boil, then cover and steam over medium heat for 40–45 minutes, until firm. Add hot water as needed so the steamer doesn’t run dry.
Cool slightly before unwrapping. Serve warm or at room temperature with crushed peanuts, if you like.