Adapted from Smitten Kitchen
Makes about 24 pirogies
1 cup water, boiled
1 medium onion, quartered
2 garlic cloves, crushed
6 ounces mushrooms, sliced (shiitakes or oysters work well)
1 ounce dried porcini
1.5 tablespoons unsalted butter
1 handful of spinach, finely chopped
1 pound onions, sliced
1/4 cup (half-stick) unsalted butter
(Note: dough makes about 48 pirogies; refrigerate extra dough for up to 3 days)
1 cup all-purpose flour, plus additional for kneading/rolling
3/4 cup cake flour (see note below)
2 large eggs
1/4 cup water
Prepare dough: Stir together the flour(s) in a bowl. Make a well in flour and add eggs, salt, and water, then stir together with fork without touching flour. Continue stirring, gradually incorporating flour into the well until a soft dough forms. Transfer dough to a lightly floured work surface and knead, adding only as much additional flour as needed to keep dough from sticking, until smooth and elastic, about 8 minutes. The dough will be soft. Cover with plastic wrap and let rest at room temperature for at least 30 minutes. (May also be made ahead: wrap well in plastic wrap and chill. Bring to room temperature before using.)
For filling: Pour boiling water over porcini in a small bowl and soak until softened, 10 to 20 minutes. Lift porcini out of water, squeezing excess liquid back into bowl, and rinse well to remove any grit. Pour soaking liquid through a paper-towel-lined sieve into a bowl and reserve. Finely chop onion and garlic in a food processor, then add mushrooms (including porcini) and pulse until very finely chopped.
Heat butter in a skillet over moderate heat until foam subsides, then cook mushroom mixture, stirring frequently, until mushrooms are dry, about 8 minutes. Add reserved soaking liquid and simmer, stirring frequently, until mixture is thick, dry, and beginning to brown, about 15 minutes. Stir in spinach and salt and pepper to taste. Cool completely.
To make the pierogies: Halve dough and roll out 1 piece on a lightly floured surface into a 15-inch round, keeping remaining dough wrapped. Cut out rounds (about 24) with floured biscuit/cookie cutter or similar. Put 1 teaspoon filling in center of each round. Working with 1 round at a time, moisten edges with water and fold in half to form a half-moon, pinching edges together to seal. Transfer pierogies as assembled to a flour-dusted kitchen towel or baking sheet. Repeat with remaining rounds.
To cook the pierogies: Begin by cooking the onions and butter in a large heavy skillet over moderately low heat, stirring frequently, until golden brown and carmelized, about 20 minutes. Season with salt and pepper and keep warm.
Meanwhile, bring a large pot of lightly salted water to boil. Gently place prepared pierogies into the boiling water and cook, covered, until tender, 12 to 15 minutes. Transfer with a slotted spoon to the skillet with your onions. Toss gently to coat and serve immediately.
[Note about cake flour: If, like me, you really don't keep cake flour on hand readily, don't freak out -- I've got you covered. Essentially, cake flour is just a much finer flour and will help your dough be less dense, more like a pastry dough. So here's what you'll want to do: measure out 3/4 cup all-purpose flour and then remove 2 tablespoons of the flour and replace it with 2 tablespoons corn starch. Finally, you'll want to sift that a few times into a bowl. This will give you the lighter flour that you're looking for.]