Bring a large pot of salted water to the boil. Add the potatoes and cook for 8-10 minutes, until they are completely tender. Drain well in a colander and allow them to dry out for a few minutes.
Place the potatoes into a large mixing bowl and add the tofu, carrot, water chestnuts, ginger, garlic and coriander. Using your hands or a large spoon, mix well, squishing and breaking up the potatoes until they are roughly mashed (your hands are the most effective for this job) and everything is well combined. Add about ½ teaspoon of salt, a good pinch of white pepper, soy sauce, and dark soy sauce and then taste, making sure it has enough flavour. Adjust seasonings if you need to. When you are happy with the flavour, shape the mixture into 8 giant round balls. They will be the size of an enlarged golf ball.
Place the cornflour onto a plate or a shallow bowl. Roll each potato ball in the cornflour so that it is completely covered. Set aside.
In a small deep pot, wok or other suitable pot for frying, add oil so that it comes 2.5-3cm (a little more than 1 inch) up the side of the pan. Heat until hot – place a wooden chopstick or spoon into the oil and if it sizzles, it is hot enough. Add about 3 balls (or however many you can comfortably fit without overcrowding) into the pan and fry on medium high heat for 2-3 minutes, and then flip the ball over and fry the other side for another 2-3 minutes, until it is golden all over. You can also use a deep fryer to cook them. When ready, place them onto a plate lined with absorbent kitchen towel or paper to soak up excess oil.
Prepare the sauce by combining the vegetable stock, soy sauce, Shaoxing wine, sugar, and cornflour (cornstarch) in a bowl or jug. Stir until the cornstarch is dissolved.
Heat a large, deep, frying pan (skillet) on medium high. Add 1 tablespoon of oil along with the garlic and ginger. Allow to sizzle for 15-30 seconds, until fragrant. Pile the lettuce into the pan, pushing it down slightly – it will look like a lot of leaves, but it cooks down considerably. Briefly stir the sauce again to make sure it’s combined and pour it over the lettuce. Place the potato balls on top of the lettuce, cover and cook on medium-high for 5 minutes.
To serve, top with green onions (scallions) and serve with rice or as part of a banquet.