Step 1: Prepare the Dough

• In a large mixing bowl, combine the flour and salt. Add the softened butter and mix it in with your hands or a pastry cutter until the mixture resembles coarse crumbs.
• In a separate bowl, whisk the egg and sour cream together until smooth. Add the wet ingredients to the flour mixture and stir to combine.
• Gradually add warm water, a tablespoon at a time, until the dough begins to come together. Knead the dough on a lightly floured surface for about 5 minutes, until it becomes smooth and elastic.
• Once kneaded, cover the dough with a clean towel and let it rest for at least 30 minutes. This will help make the dough easier to roll out and shape.

Step 2: Prepare the Filling

• While the dough is resting, heat the olive oil in a medium skillet over medium heat. Add the diced sweet potatoes, season with salt and pepper, and sauté for about 5-7 minutes until they begin to soften.
• Cover the skillet and reduce the heat to low. Continue cooking for an additional 10-15 minutes until the sweet potatoes are tender.
• Once the sweet potatoes are cooked through, transfer them to a large bowl and mash them until smooth. Stir in the shredded fontina cheese, garlic powder, nutmeg, and fresh parsley (if using). Taste the mixture and adjust the seasoning as needed. Set the filling aside.

Step 3: Roll Out the Dough

• Once the dough has rested, divide it into four equal portions. Roll out each portion on a lightly floured surface until it’s about 1/8-inch thick.
• Using a round cookie cutter (or a drinking glass), cut out circles from the dough. Aim for about 3-inch circles.
• Place about 1 tablespoon of the sweet potato filling in the center of each dough circle. Be careful not to overfill, as this can make the pierogies harder to seal.

Step 4: Seal the Pierogies

• Gently fold each dough circle in half over the filling to form a half-moon shape. Pinch the edges tightly to seal them. You can crimp the edges with a fork for an extra decorative touch.
• Repeat this process until all the dough and filling are used up.

Step 5: Cook the Pierogies

• Bring a large pot of salted water to a boil. Once the water is boiling, drop the pierogies in batches, making sure not to overcrowd the pot.
• Boil the pierogies for about 3-4 minutes, or until they float to the surface. Use a slotted spoon to remove them and transfer them to a plate.
• In a large skillet, melt the butter over medium heat. Add the cooked pierogies to the skillet and sauté them for 2-3 minutes on each side, until they are golden brown and crispy.
• Serve hot, garnished with extra fresh parsley if desired.