In a large bowl add flour, eggs, oil, salt, and 1 ½ cups of water. Mix well to form a dough, adding more water if needed.

Knead the dough on a flat surface for about 4 to 5 minutes or until it becomes smooth and pliable.

Cover the dough with plastic wrap and let it rest at room temperature for at least 30 minutes or up to 1 hour.

Peel the potatoes and cut them into 2-inch cubes. Place them in a large pot of salted water and bring to a boil. Cook the potatoes for 15 minutes or until fork tender.

While the potatoes are cooking, in a medium skillet over medium-low heat, cook the onions in 2 tablespoons butter until tender without browning.

Once the potatoes are cooked, place them in a large bowl and mash them. Add onions, cheese, and remaining butter. Continue mashing until the potatoes become very smooth.

Using half of the dough, roll it out ⅛" thick. Cut out circles of dough using a 3" cookie or biscuit cutter.

Scoop 1 ½ tablespoons of filling and roll into a ball, place on the pierogi dough. Fold the dough over to form a semi-circle and pinch the edges closed. Place on a baking sheet. Repeat.

The pierogi can either be cooked or frozen at this point.

Heat 3 tablespoons butter in a large skillet. Add diced onions and cook on medium-low heat until tender. Remove onions from the pan and set aside for serving.

Bring a large pot of salted water to a boil. Gently add pierogies and cook until they float, about 2 to 4 minutes. Remove with a slotted spoon.

Transfer pierogies to the hot skillet (adding more butter if needed) and cook until browned on each side, about 5 minutes.

Serve warm with onions and sour cream.