**Step 2: First Rise** Place the dough into a lightly oiled bowl. Cover and let rise at room temperature for approximately 1 to 1½ hours, or until doubled in volume. The exact timing will depend on the temperature of your kitchen. A properly fermented dough should look puffy, airy, and noticeably larger.

**Step 3: Prepare the Filling** While the dough rises, boil the potatoes until fork tender. Drain thoroughly. Mash until smooth and season with salt. Divide the potato mixture into two portions if desired. For one portion, stir in shredded cheese. For the second portion, mix in sautéed onions that have been cooked until golden and fragrant. Allow the filling to cool completely before shaping. Warm filling can make the dough difficult to seal.

**Step 4: Divide and Shape** Turn the dough onto a lightly oiled work surface. Divide into 70 g pieces. You should get approximately 14–15 piroshki. Shape each piece into a ball and let rest for 10 minutes. Flatten each dough ball into a circle. Place a generous spoonful of filling in the center. Bring the edges together and pinch firmly to seal. Gently flatten the shaped piroshky slightly with your hand. Place seam-side down.

**Step 5: Final Proof** Cover the shaped piroshky with a towel. Allow them to proof for 20–30 minutes. They should look slightly puffy but not over-proofed.

**Step 6: Fry the Piroshki** This step is incredibly important. Unlike many fried foods, piroshki should be fried at a lower temperature. Heat oil to approximately 320°F (160°C). A lower frying temperature allows the dough to cook completely through before the exterior becomes too dark. If the oil is too hot, the outside may brown quickly while the interior remains undercooked. Carefully place several piroshki into the hot oil. Do not overcrowd the pan. Fry until deeply golden brown on one side, then flip and continue frying until evenly golden. Transfer to a paper towel-lined tray. Serve warm.