Preheat oven to 350°F and grease a 9x13-inch baking dish.
Boil potatoes in salted water until fork-tender, about 15-20 minutes. Drain well.
In a large bowl, mash potatoes with sour cream, cream cheese, and melted butter until smooth and creamy.
Stir in 2 cups of cheddar cheese, half of the bacon, green onions, salt, and pepper.
Spread mixture into prepared baking dish and top with remaining 1 cup cheddar cheese and remaining bacon.
Bake for 25-30 minutes until heated through and cheese is melted and bubbly. Garnish with extra green onions if desired.