- Filling:
- 3 1/2 ounces dried wild mushrooms
- 2 tablespoons butter
- 1 large onion, chopped
- salt and ground black pepper to taste
- 2 tablespoons bread crumbs, or as needed (optional)
- Dough:
- 8 cups all-purpose flour
- 1 cup hot milk
- 1 egg yolk
- Place dried mushrooms in a small saucepan and cover with hot water; bring to a boil. Cook until tender, about 20 minutes. Drain and chop into small pieces.
- Melt butter in a saucepan over medium heat. Add onion; cook and stir until starting to soften, about 3 minutes. Stir in mushrooms; continue cooking until onion is soft, about 5 minutes. Season with salt and black pepper. Add breadcrumbs if filling seems too wet.
- Combine flour, hot milk, and egg yolk in a large bowl, stirring quickly with a fork until a soft and smooth dough forms.
- Roll dough out on a lightly-floured surface. Cut into 1 1/2-inch squares. Place a teaspoon of filling in the center of each square. Fold the dough over the filling to form a triangle and pinch edges to seal. Bring the bottom corners together and pinch together.
- Bring a large pot of lightly salted water to a boil. Cook dumplings in batches until they float to the surface of the water, about 10 minutes. Transfer to a serving plate with a slotted spoon.