DOUGH: To prepare dough, place flour and sea salt in a medium mixing bowl and mix. Add water and oil. Mix with a spoon until cool. Using your hands, form a ball of dough. Place dough on a lightly floured surface and knead 2 to 3 minutes. Place back in mixing bowl, cover, and refrigerate for 30 minutes.
CARAMELIZED ONIONS: Heat oil in a heavy skillet and sauté onions with a pinch of sea salt until translucent and golden brown. Stirring frequently. Set aside.
BOIL POTATOES: Place potatoes in a pan with water to cover and add a pinch of salt. Bring to a boil. Reduce heat to medium and simmer until potatoes are tender. Remove, pour into a colander, and drain water. Divide in half for each type of filling. Set aside to cool.
MUSHROOM FILLING: Place 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 fresh mushrooms with the soy sauce for about 2 to 3 minutes. Add the maitake, shiitake, and garlic. Sauté 3 to 5 minutes. Add 1 1/2 cups of cooked potatoes and mash with a potato masher or fork. Add 1/2 cup caramelized onions, sauerkraut, black pepper, and sea salt. Mix well. Set filling aside.
POTATO FILLING: Heat oil and sauté onions until translucent. Add 1 1/2 cups cooked potatoes and mash with a potato masher or fork. Add remaining half of the caramelized onions, sauerkraut, salt, and pepper. Mix.
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 pierogi shell. To form the pierogi, place 1 1/2 to 2 teaspoons of filling in the center of each dough circle. Moisten edge of half the dough with a little water, fold it over the filling, and pinch the edges together firmly. Repeat, alternating fillings. Keep the filled pierogi covered until all have been formed.
BOILING PIEROGI: Bring 3 to 4 quarts of water to boil in a medium pot. Working in batches of 5 or 6, cook pierogi in boiling water until they float to the surface - about 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 pierogi until golden brown on each side. Continue boiling and frying the pierogi until all have been cooked.
Serve with sauerkraut.
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