Melt butter in a skillet over medium heat. Add chopped bacon and onions; cook until bacon is crisp and onions are browned. Reserve about 2 tablespoons of the bacon fat and remove the rest to a small dish.

Place potatoes into a large pot and cover with salted water. Bring to a boil, then reduce heat and simmer until tender. Drain and mash until smooth. Let cool for 10 minutes.

Season mashed potatoes with salt, black pepper, and cayenne pepper. Stir in 1 egg and farmer's cheese. Cover and refrigerate until chilled.

Beat 1 egg with 1 tablespoon water in a bowl to create the egg wash.

Place 2 to 3 wonton wrappers on a floured surface. Brush edges with egg wash, add about 2 tablespoons of filling to each. Fold and seal each pierogi.

Bring a pot of salted water to a boil. Cook pierogi until they float (about 2–3 minutes) and drain.

Heat reserved bacon drippings in a skillet. Cook pierogi until browned (about 2 minutes per side). Toss with cooked bacon and onions.