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 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 3 minutes per side.
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.