Dough

1. Mix the flour and salt in a food processor. Add the eggs, butter and water (starting with 3/4 cups if the dough is dry, adding 1 tablespoon at a time until the dough is smooth and elastic, adding up to an additional 3/4 cup if needed) pulsing until kneaded by machine and a ball is formed, or you can use a mixer to do this process.
2. Remove dough from bowl and let sit in a warm place for about 15 to 30 minutes.

Filling

1. Melt butter in a large fry pan and add onions. Sauté until onions are lightly browned; set aside.
2. Combine potatoes, cheese, salt, pepper and as much of the sautéed onions as you like, reserving the rest to toss with cooked pierogi. Taste for seasoning. Set aside.
3. Divide dough into 3 to 4 equal portions. On a lightly floured surface, roll one portion of dough out to about 1/8-inch thickness. Cut a 3-inch round circle with biscuit cutter. Place one tablespoon of filling on one side of each round. Using your finger, moisten one side of dough with some water. Pick up the circle and fold dough over filling and pinch edges together to firmly seal the filling (this is critical – if you don’t pinch the dough together tightly, you will have gaps and when you boil the pierogi, the filling will come out).
4. Place the filled pierogi onto a lightly floured baking pan; cover until you finish with remaining dough and filling.
5. In a large wide pot, fill with water and bring to a boil over medium to high heat, when water is at a rolling boil, drop 5 to 6 pierogi and cook while stirring gently with a wooden spoon until they float to the top of pot. Cook a couple minutes longer.
6. Remove with a slotted spoon, toss with reserved sautéed onions, if desired, and place in a warmed deep glass bowl.
7. If desired, saute the pierogi briefly in a small amount of equal amounts of olive oil and butter (as shown in photo).
8. Serve warm with some sour cream on the side.