To soften the banana leaves and prevent them splitting ,put them in a hot oven for about 10 to 20 seconds, or blanch them briefly. Cut the leaves into 12 circles 15cm (6 inches) in diameter with the fiber running lengthways. Place one piece with the fiber running lengthways and another on top with the fibre running across. Make a 1 cm (1/2 inch) deep tuck 4 cm (1 1/2 inches) long (4 cm in from the edge and no further) and pin securely with a small sharp toothpick.