Melt butter in a large skillet over medium heat. Add chopped bacon and onions; cook and stir until the bacon is crisp and the onions are browned, 6 to 8 minutes. Remove bacon and onions to a small dish, reserving about 2 tablespoons of the bacon fat for frying the pierogi.
Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain and mash until smooth. Allow to cool for 10 minutes. Season with Fire and Smokes Society Potato Slayer, cayenne pepper and salt and pepper. Stir in 1 egg and cheddar cheese. Cover and refrigerate until chilled, about 30 minutes.
Beat egg with 1 tablespoon water in a bowl for the egg wash.
Place 2 to 3 wonton wrappers at a time on a lightly floured work surface. Brush the edges lightly with the egg wash. Place about 2 tablespoons of filling in the center of each wrapper. Fold each pierogi in half and lightly press the edges together to seal.
Bring a pot of salted water to a boil and cook pierogi in the boiling water until they float, 2 to 3 minutes. Drain.
Transfer pierogi to the skillet with reserved bacon drippings in batches and cook over medium heat until lightly browned, about 2 minutes per side. Transfer to a bowl, toss with the bacon and onions. Top with sourcream and garnish with chives.