Begin by peeling and chopping three large potatoes into even chunks. Place them in a large pot, cover with salted water, and bring to a boil. Cook for approximately 25 minutes, or until fork-tender. Drain the potatoes and set them aside to cool slightly while you proceed with the other steps.

In a large skillet over medium heat, fry eight slices of bacon until crispy and golden, about 8-10 minutes. Once cooked, remove the bacon and place it on paper towels to drain. Reserve a tablespoon of the rendered fat in the pan for adding flavor to the next layers of your Pierogi Lasagna.

Using the skillet with the reserved bacon fat, add two diced large onions. Cook the onions on medium-low heat for about 15-20 minutes, stirring occasionally, until they become deeply browned and fragrant.

In a large mixing bowl, mash the boiled potatoes until smooth. Stir in minced garlic, 16 ounces of sour cream, ¼ cup of butter, 1 cup of milk, and 1 cup of cream, blending until creamy. Season generously with salt and pepper to taste.

Bring a large pot of salted water to a boil and cook the lasagna noodles for 5 minutes less than the package instructions recommend, roughly 8-9 minutes. Drain the noodles and toss them with a drizzle of oil to prevent sticking.

In a large baking dish, spread a layer of the creamy potato sauce on the bottom. Place a layer of noodles over the sauce, followed by a portion of the caramelized onions, crispy bacon, and a sprinkle of cheddar cheese. Repeat the layers until you run out of ingredients, finishing with a layer of noodles topped generously with remaining cheese.

Preheat your oven to 350°F (175°C). Cover the baking dish with aluminum foil and bake the Pierogi Lasagna for about 30 minutes. Once heated through, remove the foil and bake for an additional 10 minutes to allow the top to become bubbly and golden.

Once baked, remove the Pierogi Lasagna from the oven and let it cool for about 10 minutes. Just before serving, top with the remaining crispy bacon and freshly sliced scallions.