Place potatoes in a pot, cover with water, and bring to a boil over medium/high heat. Cook uncovered for 20-25 minutes, or until easily pierced with a fork. Drain, let cool for 5 minutes, and then mash the potatoes.

Add to mashed potatoes the salt, melted butter, cream cheese, and mozzarella cheese; mix well. Cover and set aside.

In a large mixing bowl, whisk together water, milk, sour cream, egg, and salt until blended. Add 2 cups of flour and mix in. Add remaining flour ½ cup at a time, making sure it all blends in. For last ½ cup of flour, add only 1 TBSP at a time, until just until dough is not sticking to sides of the bowl.

Knead by hand for 3 – 5 minutes, until dough is smooth and elastic.

Divide the dough in half. Wrap one half in plastic wrap. Roll out the other half on a floured surface until just under 1/8” thick. Use cookie cutter to cut out circles of dough. Collect the scraps, re-form the dough into a circle, roll out, and repeat.

Repeat this process with the 2nd half of the dough until you have 55 – 60 dough circles.

Add ½ TBSP of the potato mixture to each circle. Fold over and pinch edges to seal; pinch and twist around the edges to fully seal.

Cook the bacon and melt the butter before you boil the pierogi. You’ll want this topping to be ready to help keep pierogi from sticking after they cook.

Using a medium skillet, sauté the chopped bacon until crisp, then add the butter to melt. Remove pan from heat and set aside.

Bring a large pot of water to a rolling boil. Add 1 TBSP of salt. Add as many pierogi as you can fit to have one layer without overcrowding. Let water return to a boil, then cook 3 – 5 minutes, until dough is very tender. Remove from water with a slotted spoon, placing in a large bowl or glass serving dish. Drizzle the bacon and butter topping over each layer to reduce sticking. Repeat, continuing to cook in batches.