1. Prepare the Dough: Mix flour, beaten eggs, oil, salt, and 1 ½ cups water in a large bowl. Add additional water gradually if the dough is too dry. Knead the dough on a lightly floured surface for 4–5 minutes until smooth and pliable. Cover and let rest for 30 minutes to 1 hour at room temperature.

2. Make the Filling: Boil peeled potato chunks in salted water until fork-tender (about 15 minutes). Drain well, then mash potatoes until smooth. In a skillet, gently sauté the diced onion in half the butter over medium-low heat until soft but not browned. Combine the mashed potatoes with sautéed onions, shredded cheddar cheese, remaining butter, salt, and pepper. Mix well and cool the filling thoroughly—ideally refrigerate for at least 30 minutes to firm up.

3. Assemble Pierogi: Roll out half the dough on a floured surface to approximately ⅛ inch (about 3 mm) thickness. Use a 3-inch (7.5 cm) round cutter to cut circles. Place about 1 ½ tablespoons of filling in the center of each circle. Moisten the edge of the dough with water, fold over into a semi-circle, and press edges tightly to seal. Repeat with remaining dough and filling to yield approximately 65 pierogi.

4. Cook Pierogi: Bring a large pot of salted water to a boil. Cook pierogi in batches to avoid crowding; boil for 2-4 minutes or until they float to the surface. Remove with a slotted spoon and drain. For added texture and flavor, pan-fry boiled pierogi in butter until golden and crispy on each side.

5. Prepare Onion Topping: In a pan, sauté diced onion in butter over medium heat until translucent and slightly golden. Use as a topping for serving.

6. Serve: Plate pierogi, top with sautéed onions, and garnish with sour cream and optionally chopped parsley or chives. Serve warm.