Taking a main leaf, form a cone on one end with the raised side of the central rib facing outward. Grip the edges tightly with your non-dominant hand to hold the shape.
Add either fava or red bean rice mixture to the cup, then use your dominant hand to fold the leaf over and around the cone while keeping your other hand in place. This will create the “little foot” shape while leaving an opening where the “ankle” is.
Use the ankle hole to fill in more rice and beans, and tamp down using a chopstick. Make sure the bamboo leaf is tightly filled, as this makes the zongzi easier to wrap and less likely to come undone while cooking.
Select a helper leaf that is wide enough to cover the ankle hole. Place one end of the helper leaf under the “foot,” with the rest of the leaf trailing off the back. Wrap the leaf up the back of the foot and over the ankle hole, sealing it, and continue wrapping down one side of the foot, and underneath, following the contour of the foot. When you get to the end, tuck it in one of the folds. Don’t worry if it’s a little loose.
Take a segment of kitchen twine and clamp down on one end with your teeth. Holding the zongzi in front of you with one hand, use the other to wrap the string around the zongzi. Knot tightly, digging the string into the zongzi.
Repeat with remaining rice and bamboo leaves. If any main leaves crack or split during the wrapping, start over and recycle it as a helper leaf.