Heat a couple of tablespoons of oil in a nonstick skillet over medium high heat. Sauté the cabbage until softened, about 5 minutes. Set aside the cabbage in a large mixing bowl.

Heat a tablespoon of oil in the same skillet. Sauté the scallions and ginger until the scallions turn a bright green, about 30 seconds. Add the cooked scallions into the same mixing bowl.

Heat a few tablespoons of oil in the same skillet. Add the mushrooms and sauté for about 5 minutes, about the moment when the liquid starts to evaporate. Add the cooked mushrooms to the large mixing bowl.

To the same bowl, add garlic, sesame seed oil, and soy sauce. Add a few grinds of black pepper and a pinch of salt. Mix thoroughly. Taste and adjust seasonings. If the mixture is still hot, let cool a bit before adding the egg yolk.

Once the mixture has cooled, add the egg yolk and bread crumbs to the mixture and mix thoroughly.

Line a large baking sheet with a sheet of parchment paper. Set up the wonton skins next to the bowl of mushroom mixture.

Dip half of the wonton skin into the egg white so that a thin film cover half of one side of the skin. Spoon about 1 1/2 teaspoons of the mixture onto the middle of the square. Fold the skin in half and press the edges to seal the mandoo. Lay the mandoo on the baking sheet. Repeat until the rest of the wonton skins are filled and sealed. Make sure the dumplings are not laying on top of each, otherwise they will stick together and you’ll create a big sticky mess.

The mandoo is ready to use right away or you can freeze them for later use. To use later, freeze on the baking sheet until frozen solid. Store the mandoo in a sealable food storage bag. You do not need to thaw out the mandoo before using, cook them as you would “fresh” mandoo.

Yaki mandoo (potstickers): Heat a couple of tablespoons of cooking oil in a nonstick skillet over medium heat. Add the mandoo (frozen of fresh) to the skillet, but do not lay them on top of each other. Let them turn a golden brown on one side. Do not flip them over. Add about a 1/4 cup of water and cover the pan immediately. Let cook for about 1-2 minutes. Uncover and let the remaining water in the pan evaporate. The mandoo is done once the wonton skin turns wrinkly and translucent. Carefully scoop the mandoo out with a spatula. Serve with the Easy Peasy Dipping Sauce (recipe below).

Boiled mandoo: Bring a medium-size pot of water to boil. Use enough water that will give the mandoo enough room to float around. Once the water starts boiling, add mandoo to the water. The mandoo is done once they float to the surface and the skin over the filling turns wrinkly and translucent. Scoop the mandoo out with a slotted spoon into a serving bowl. Serve with the dipping sauce.