In a bowl, mix the pork with the garlic, scallion, 1 1/2 tablespoons of nuac mam, 1/2 teaspoon sugar, egg, and cornstarch. Leave in refrigerator for 1/2 hour. Meanwhile, prepare the charcoal fire (or heat indoor grill).
When grill is heated, shape the pork mixture into 6 balls. Lightly oil a steamer tray and steam balls for 5 minutes. Transfer partially cooked balls to a hot grill fire. Cook for 10 minutes, turning occasionally, so all sides of the pork balls get golden brown. Remove pork balls from fire, cut them in half, and return them to fire, cut side down. Grill for 5 minutes. Remove pork and, when cool enough to handle, cut in shreds roughly 1 1/2 inches long and 1/4-inch thick. Reserve.
Bring a few quarts of salted water to a boil. Plunge the shrimp into the boiling water then turn the heat off. Remove shrimp from water when just cooked (about 2 to 3 minutes). In a bowl, mix 2 tablespoons fish sauce and remaining tablespoon of sugar. When shrimp are cool enough to handle, peel and slice them in half the long way (cutting the shrimp into 2 thin, C-shaped pieces). Reserve shrimp and fish sauce mixture.
Dip one sheet of banh trang into a basin of warm water, keep it submerged for 2 to 3 seconds, then remove it immediately from the water. Try to dip all of it into the water simultaneously, and handle it carefully so it doesn't tear. Place the sheet on a dry towel.
About 1-inch above the lower edge of the sheet, spread out 1/8 cup of shredded lettuce. Leave a 1 1/2-inch gap between the left edge of the sheet and the lettuce, and a 1 1/2-inch gap between the right edge of the sheet and the lettuce. Define a rectangle with the lettuce that's about 5 inches wide and 3 inches in the other direction (towards the center of the sheet). Now evenly top the lettuce rectangle with 1/8 of the bean sprouts, 1/8 of the carrots and 1/8 of the peanuts. Evenly distribute 1/8 of the pork over the rectangle. Tear 5 to 6 mint leaves and an equal amount of cilantro, and distribute over the rectangle. Top everything with a few sprinkles of nuoc mam.
Carefully pick up the right edge of the sheet, and fold it leftward toward the center of the filling. Make sure the folded sheet is even and uncreased everywhere. Do the same with the left edge of the sheet. The rectangle of the filling should now be covered by the folded sheet. Pick up the bottom edge of the sheet, and start rolling away from you, towards the top edge, making sure to tuck the filling in tightly as you roll. When you have rolled about halfway to the top of the sheet, dip the shrimp halves in reserved fish sauce/sugar mix. Place 2 shrimp halves along the cylinder that you have half-rolled, and keep on rolling until a fully rolled cylinder is formed. Place under a wet towel. Repeat process 7 more times. Serve immediately, or cover rolls with wet towels and save at room temperature for several hours. Serve with Vietnamese peanut sauce.
*Banh trang, or Vietnamese spring roll wrappers, come in both round and square shapes. The square is easier to work with when making summer rolls.