Peel and dice potatoes, fill a stock pot with water and add potatoes and salt to the water. Boil the potatoes until they are fully cooked, or you can easily puncture them with a fork with no resistance
While the potatoes are cooking, saute the onions in a fry pan using a little butter and some of the drippings from the bacon. You want the onions to brown and caramelized.
Drain water from the cooked potatoes and use a potato masher to mash them. Add the cheddar cheese, cream cheese. Then, mix together until the cheese is fully melted and set aside until cooled. Once cooled, form the cheese and potato mixture into ½ to 2 inch balls.
While the potato mixture is cooling begin to make the dough. In a mixing bowl, add the flour, eggs, salt, and sour cream. Using a fork, stir the ingredients together. You will want to use your hands at some point to fully incorporate the ingredients.
The dough should start to come together. If it does not, add a little more sour cream or a little milk. Once it begins to come together, place on a floured surface and kneed the dough until it comes completely together.
Wrap the dough in some plastic wrap and place in the refrigerator and allow to rest for at least 30 minutes to an hour.
Next, take the dough out of the refrigerator and roll out on a floured surface until the dough is approximately ⅛ of an inch. (Don't get too caught up in the thickness. You want it to be workable and not too thin that the dough will puncture when you are filling it.)
FYI: Dough should be somewhat elastic while you are rolling it out. This means that it should spring back as you are rolling it out into a circle.
Use a drinking glass to cut circles out of the dough. Place your filing ball in the center of the dough and Fold the dough over the filling. You will need to stretch the dough over to seal. Using your fingers, pinch the dough closed.
If the dough does not seal, wet your finger and run your finger on the edge of the dough. This should act as a "glue" to seal your dough. You can also use a back of a fork to help seal your edges. This gives the Pierogi a very nice look.
Your finished Pierogi will have a semi-circle appearance. Set aside and continue to make the rest of your Pierogi.
Fill a stock pot with salted water and bring to a boil and then add a few Pierogi at a time. Allow Pierogi to cook in the boiling water until the Pierogi float to the top. This will take a few minutes. Remove from water and place on a cooling rack to drain and cool. Continue this process until done with all Pierogi.
When ready to eat, fry in butter in a pan over medium heat until Pierogi are golden brown on both sides. Serve with sour cream and chopped green onion stems (optional)
Important Tips for Making the Best Homemade Pierogies
If using leftover mashed potatoes to make pierogi, do not add butter to the filling.
While you are rolling out the pierogi dough, you’re looking for a little elasticity in the dough; you want it to spring back a bit while as you roll it out.
When you place the filling on the dough to make these Polish dumplings, you are going to have to stretch the top edge of the dough to envelop the pierogi filling.
You may need just a bit of water on your fingertips to help seal each pierogi tightly.