Wash banana leaves and remove central stems.
Cut leaves into 5-inch (13 cm) squares.
Bring a large pot of water to boil. Add leaves and blanch for about 10 seconds to soften. Remove and run under water to cool. Set aside.
Combine all remaining ingredients, mixing to make a very soft dough. Add a little extra water if dough is too stiff, or add flour if dough is too liquid.
Place about 1/2 cup dough on each leaf. Fold to make a neat parcel. Secure by tying with kitchen twine or leftover strips of banana leaf. Dough can also be wrapped in aluminum foil if banana leaves are unavailable.
Bring a large pot of water to a boil. Add ducuna packets and simmer for about 45 minutes. Drain and allow to cool.
Serve warm or at room temperature.