Bring a large saucepan of salted water to a boil, add the potatoes and cook until completely soft. Drain and set aside to dry out for 3-5 minutes, then mash the potato.
In a large frying pan over medium heat, add a drizzle of oil, along with the ginger, garlic and leek, and season with sea salt and white pepper. Sauté, stirring constantly to prevent burning, for 3-4 minutes until the leek is translucent. Remove from the heat and stir in the mashed potato. Taste and season with sea salt and white pepper. Now your filling is ready.
If using store-bought wrappers, you will need to wet the edges to get them to stick. If you are using homemade dough, it will be soft enough to crimp without wetting the edges. Fill the wrappers with 1-2 tablespoons of filling then pleat the edges to make a crescent shape. Or use your own favorite dumpling-folding method.
To make potstickers, heat a nonstick skillet over medium heat with just a teaspoon of oil. Make sure your skillet has a tight-fitting lid. When the skillet is hot, arrange the dumplings in a chrysanthemum pattern in the skillet, starting in the center with a starburst shape, and adding dumplings close together as you create a tight-fitting flower. Fry until the bottoms are golden brown. You will need to lift one dumping up to check the color underneath.
In a small bowl, combine 1 teaspoon of cornstarch with 1/3 cup cold water. Quickly pour the cornstarch water over the dumplings, cover with a lid, and lower the heat to low. When the water has evaporated, the dumplings are finished. Listen, and you will hear the sounds in the skillet change when the last drops have evaporated. Remove the lid. Turn off the eat. Place a dinner place face down over the dumplings in a skillet, and then with one hand on the back of the plate, and with speed and coordination, flip the skillet upside down so the dumplings appear on the plate. If cooked in the chrysanthemum pattern, they will look lovely with a lacy frill from the cornstarch.
Serve with a spicy dipping sauce like chili oil or garlic achaar.