Prepare the pierogi dough using your favorite recipe or use the best pierogi dough recipe.
Peel and chop an onion, and saute it with a few tablespoons of oil in a non-stick skillet over medium heat for 6 to 10 minutes until soft and cooked.
Add the ground meat, salt, pepper, or any other spices that you like. Cook for 10-15 minutes until browned.
Taste and adjust seasoning if needed.
Let the meat cool down a bit, and then stir in a whisked egg to bind everything together.
Grind the meat mixture in a food processor, meat grinder, or blender until it turns into a paste.
Divide the pierogi dough into two or three parts. Then, spread one on a floured work surface and roll it out until it's thin. It shouldn't be super thin so that you can still stretch it when forming the pockets.
Cut palm-sized circles in the rolled pierogi dough using a cookie cutter or glass.
Place a spoonful of meat filling in the center of each dough circle. Fold the dough over the filling and press the edges together, starting in the middle. Leave as little air as possible in the pocket you're forming. To help form a good seal, moisten the outer edge of the dough using a wet finger.
Place each formed pierogi on a floured cookie sheet and cover them with a damp kitchen towel.
Bring a large pot of salted water to a boil. I typically use one teaspoon of salt per quart of water but feel free to adjust the amount to your preferences.
Once the water is boiling, add a few pierogi to the pot and stir them to prevent them from sticking to the bottom. Once the pierogi start floating to the surface, simmer them gently for another 3 to 4 minutes. Make sure not to overcrowd the pot so that the pierogi don't stick together or cook unevenly.
Remove the pierogi from the water using a slotted spoon and serve immediately with your favorite toppings.