1. Using a damp towel, wipe the banana leaf clean on both sides. Cut out 4-by-4-inch squares from the banana leaf. Set aside on a baking sheet. Brush one side lightly with oil.

2. To make the batter, sift the rice flour, all-purpose flour, baking powder, and salt in a large bowl. In a medium bowl, beat the egg with ¾ cup water, then stir this into the dry ingredients, to form a thick but smooth batter. Refrigerate the batter for 30 minutes to 1 hour.

3. Fill a deep saucepan or wok with 3 inches canola oil and warm over medium heat until the temperature is between 350°F and 365°F.

4. While the oil is heating, prepare the filling: Combine the Napa cabbage, carrots, snowpeas, leeks, bean sprouts, shrimp, fish sauce, and black pepper in a large bowl. Stir the batter and pour just enought into the filling to coat the ingredients. Sprinkle 1 to 2 tablespoons over the mixture and toss to firm it up if necessary (it should not be too wet).

5. Put about 1/3 cup of the filling on the oiled side of each banana leaf square. Place a square on a spider and lower it into the oil. Fry until the fritter is set (about 1 minute), lift from the oil, and remove the banana leaf. Continue frying for another minute until the fritter is lightly browned. Flip and brown the other side until crisp, 1½ to 2 minutes. Life out of the oil with the pider and place on a paper towel-lined baking sheet to drain. Repeat until all the filling is fried. Serve hot with the vinegar dipping sauce.