1, Fill the steamer pan halfway with water and bring to a rolling boil over high heat. Meanwhile, put the paste, fatback, and pepper in a bowl. Use a rubber spatula to mix well, making sure the pork fat is evenly distributed. Deposit all the paste in the center of the banana leaf and use the spatula to spread it into a disk 6 inches in diameter and 1 inch thick. Wet your palm with water and rub it in a circular motion to smooth the top. Wet your fingers and smooth the sides.
2, Lift up the leaf, place it in the steamer tray, and place the tray in the steamer. Cover and steam for 20 to 25 minutes, or until a toothpick inserted in the center comes out clean. Turn off the heat and uncover. When the steam has dissipated, transfer the sausage on the leaf to a rack and let cool completely. Fresh from the steamer, the sausage will be white and slightly inflated. As it cools, it returns to its original size and the outside turns pale yellow. (The steamed sausage may be well wrapped and refrigerated for up to 1 week. Return it to room temperature before proceeding.)
3, You may deep-fry or bake the sausage for the final cooking. Traditionally it is deep-fried, which yields great color, while baking, of course, is easier. Cut the sausage into 3 fairly long pieces that will yield nice slices when cut. To deep-fry, pour oil to a depth of 1½ inches into a wok or Dutch oven and heat to 350°F on a deep-frying thermometer. (If you don’t have a thermometer, stand a dry bamboo chopstick in the oil; if small bubbles immediately gather on the surface around the chopstick, the oil is ready.) Add the sausage pieces and fry, turning with tongs for even coloring, for about 4 minutes, or until golden and crisp. Using tongs, transfer to paper towels to drain, blot with more towels, and let cool for 1 to 2 minutes.
To bake, place the 3 sausage pieces in a toaster oven set to the highest heat (broil) and cook, for about 4 minutes on each side, or until golden and crisp. The pieces will hiss and pop, so monitor closely to prevent charring. The color isn’t as even with baking as it is with deep-frying and the sausage takes longer to cook, but there is typically less hassle for the cook. Remove from the toaster oven, briefly blot with paper towels, and let cool for 1 to 2 minutes.
4, To serve, slice into ¼-inch-thick pieces and serve piping hot.