DOUGH: To prepare the dough, place the flour and sea salt in a medium mixing bowl and mix to blend. Add the water and oil. Mix with a spoon until cool. Using your hands, form a ball of dough. Place the dough on a lightly floured surface and knead for 2 to 3 minutes. Place back in the mixing bowl, cover and refrigerate for 30 minutes.
CARAMELIZED ONION: Heat the oil in a heavy skillet and sauté the onions with a pinch of sea salt until translucent and golden brown while stirring frequently. Set aside.
BOIL POTATOES: Place the potatoes in a pan with water to cover and add a pinch of salt. Bring to a boil. Reduce the heat to medium and simmer until the potatoes are tender. Remove, pour into a colander and drain the water. Divide in half for each filling and set aside to cool.
MUSHROOM FILLING: Place the maitake and shiitake in a small saucepan and cover with cold water. Bring to a boil. Reduce heat and simmer for 10 minutes. Remove, drain, and coarsely chop. Heat oil in a skillet and sauté the fresh mushrooms with the soy sauce for about 2 to 3 minutes. Add the maitake, shiitake and garlic. Sauté another 3 to 5 minutes. Add 1 1/2 cups of the cooked potatoes and mash with a potato masher or fork. Add 1/2 cup caramelized onions, sauerkraut, black pepper and sea salt. Mix well. Remove and set filling aside.
POTATO FILLING: Heat the oil and sauté the onions until translucent. Add 1 1/2 cups cooked potatoes and mash with a potato masher or fork. Add the remaining half of the caramelized onions, sauerkraut, salt and pepper. Mix to combine.
ROLLING DOUGH AND FORMING PIEROGI: Divide the dough into thirds and roll out on a lightly floured surface until about 1/8-inch thick. Using a pastry cutter or glass, cut the dough into 3 to 3 1/2-inch circles for the wrapper. To form the pierogi, place 1 1/2 to 2 teaspoons of the filling in the center of each wrapper. Moisten the edge of half the dough with a little water, fold it over the filling, and pinch the edges together firmly. Repeat, alternating fillings, keeping the filled pierogi covered until all have been formed.
BOILING PIEROGI: Bring 3 to 4 quarts of water to a boil in a medium pot. Working in batches of 5 or 6, cook the pierogi in boiling water until they float to the surface - 3 to 4 minutes. Remove and drain in a colander. Repeat until all pierogi have been boiled.
FRYING PIEROGI: Heat 2 to 3 tablespoons oil in a heavy skillet and fry the pierogi until golden brown on each side. Serve with a little sauerkraut. Continue boiling and frying the pierogi until all have been cooked.
Per serving - 119 calories, 5 g fat (36% calories from fat), 2 g protein, 17 g carbohydrate, 1 g fiber, 0 mg cholesterol, 76 mg sodium