Making Roasted Butternut Squash Feta Pierogi involves several parts, from preparing the filling to assembling the dough. Follow these steps to create your delicious pierogi:

1. Roast the Squash: Preheat your oven to 400°F (200°C). Cut the butternut squash in half lengthwise and remove the seeds. Drizzle with olive oil, salt, and pepper. Place cut-side down on a baking sheet and roast for 30-40 minutes, until tender.
2. Mash the Squash: Once the squash is cool enough to handle, scoop the flesh into a bowl and mash it until smooth. Add the crumbled feta and nutmeg, mixing until well combined.
3. Make the Dough: In a large bowl, mix the flour and salt. Make a well in the center and add the egg and half of the water. Combine until a dough forms. Add additional water as necessary to create a smooth, pliable dough.
4. Knead the Dough: Turn the dough onto a floured surface and knead for about 5 minutes until smooth. Wrap in plastic wrap and let it rest for 20 minutes.
5. Roll Out the Dough: Divide the dough into four sections. Roll out one section on a floured surface to about 1/8 inch thickness. Use a round cutter (about 3 inches in diameter) to cut out circles.
6. Fill the Pierogi: Place a small spoonful of the butternut squash filling in the center of each dough circle. Fold the dough over and pinch the edges to seal tightly, making sure there are no air pockets.
7. Cook the Pierogi: Bring a large pot of salted water to a boil. Drop the pierogi into the boiling water in batches, being careful not to overcrowd. Cook for about 3-4 minutes or until they float to the surface. Remove with a slotted spoon.
8. Fry the Pierogi (Optional): In a skillet, melt the butter over medium heat. Add the boiled pierogi and fry until golden and crispy on the outside, about 2-3 minutes per side.
9. Serve: Plate the pierogi while hot, garnishing with fresh herbs and serving with a dollop of sour cream, if desired.