Bring a large pot of lightly salted water to a boil. Add frozen perogies and boil for about 3 minutes or until they float to the top.
Meanwhile, cook bacon and onion in a large skillet over medium-high heat until both are lightly browned.
Remove cooked perogies to a plate lined with paper towel.
Add butter to skillet with bacon and onions, then add perogies in a single layer and brown on both sides, about 2-3 minutes per side.
Reduce the heat to medium. Whisk together cream, salt and pepper and add to the hot pan once perogies are lightly browned. Let simmer for 2-3 minutes until thickened slightly (it will bubble up and thicken fairly quickly, so keep an eye on it!).
Remove from the heat to garnish with green onions if desired and serve.
Notes
Ingredients and Substitutions:Bacon: you can omit the bacon if you prefer for a meatless meal or side dish.Cream: I recommend heavy whipping cream because it thickens into a rich sauce without corn starch. To use a lighter cream or milk, you'll likely have to use corn starch or flour to thicken.