The key to pirozhki is soft, fluffy yeast dough and a well-seasoned filling. Fillings must be cooled before stuffing to prevent soaking the dough. Baked pirozhki are a healthier version, which are brushed with egg at the end for a beautiful shine.
When stuffing, it is important to seal the edges thoroughly so that the filling does not leak out during baking.
In a bowl, mix lukewarm milk with sugar and yeast. Let the starter rise (10 minutes).
In a large bowl, mix flour, salt, and egg. Add the starter and melted butter. Knead into a smooth and elastic dough. Cover the dough and let it proof in a warm place for 90 minutes until it doubles in volume.
Meat Filling: Sauté the onion in oil, add the ground meat and brown. Season with salt and pepper. Let cool.
Cabbage Filling: Sauté the onion in oil until translucent. Add the drained sauerkraut and simmer until soft (about 15-20 minutes). Season with salt and pepper. Let cool.
Lightly knead the risen dough. Divide it into 15 equal pieces (about 60 g each). Form each piece into a ball.
Roll out or flatten each ball into an oval shape (or circle) about 5 mm thick. Place a spoonful of the cooled filling in the center.
Fold the edges of the dough over and seal them thoroughly to form a boat or half-moon shape with a smooth seam on top. You can crimp the seam decoratively if desired.
Arrange the Pirozhki on a baking sheet lined with parchment paper, let them proof for 15 minutes. Preheat the oven to 185 °C (365 °F).
Brush with the whisked egg (for brushing) and bake for 18-20 minutes until golden brown and glossy.
Let the Pirozhki cool slightly on a wire rack. Serve warm, perhaps with a glass of milk or as a side dish to Shchi soup.