Prepare the Rice Batter: In a medium pot, combine the Banh Gio flour and pork stock over medium-high heat. As it cooks, the mixture will start to thicken. Stir frequently until you reach the consistency of creamy mashed potatoes (about 15 minutes from start of heating). Turn off heat and set aside. If you see clumps, stir vigorously to smooth them out. You can also use an electric hand whisk to make stirring easier.

Make the Filling: Heat 2 tablespoons of oil in a large skillet over medium-high heat. Add the ground pork, onions, garlic, wood ear mushrooms, oyster sauce, and ground black pepper. Cook for about 5 minutes, then set aside.

Assemble the Dumplings: Use two banana leaves for each dumpling. Overlap them partially, if needed, to create more surface area. Fold the leaves into a cone, pressing down where you want the tip, then bring the sides together. Using a spoon greased with oil, add about 1/3 cup batter to the bottom of the cone. Spread the batter up the sides to form a well. Add 2 tablespoons pork filling and a quail egg, then top with a more batter. Smooth the surface. Fold the banana leaves over to form a four-sided base. Wrap tightly in plastic wrap and repeat.

Steam the Dumplings: Place the wrapped dumplings in a steamer and steam for 30 minutes.

Serve: Enjoy the dumplings plain, with light soy sauce, or with a Vietnamese fish-sauce dipping sauce (Nuoc Cham).