Drain the soaked glutinous rice well. In a large bowl, mix it with the coconut milk, sugar, salt, and cooked black beans until evenly combined. Let it sit for 15 minutes so the rice soaks up the liquid.

Wipe the banana leaves clean with a damp cloth. If using frozen leaves, pass each one over a flame or hot pan for a few seconds until glossy and pliable, then cut to size.

Quarter the peeled bananas lengthwise and crosswise into about 20 pieces total, roughly the length of a finger.

Lay one banana leaf flat, shiny side up. Spoon about 3 to 4 tablespoons of the rice mixture into the center.

Place 2 banana pieces on top of the rice, then cover completely with another 2 to 3 tablespoons of rice mixture so the banana is fully encased.

Fold the leaf over the filling into a tight rectangular parcel, then fold in the ends. Wrap a second leaf around it in the opposite direction for structure and tie snugly with string.

Repeat with the remaining rice, banana, and leaves to make about 10 parcels.

Arrange the parcels in the 8-quart / 7.6 L stockpot and cover completely with water. Set a small plate on top to keep the parcels submerged.

Bring to a boil, then reduce to a steady simmer. Cook for 90 minutes, topping up with boiling water as needed to keep the parcels covered.

At the 75 minute mark, lift one parcel out and partly unwrap it. The rice should look glossy and dense, not chalky or dry in the center.

Remove the parcels with tongs and drain. Cool on a rack for at least 20 minutes before unwrapping and slicing to serve.