Preheat the oven to 375°F (190°C).
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Peel and dice the russet potatoes into small cubes.
Boil the potatoes in a large pot until fork-tender. Drain and set aside.
In a large mixing bowl, combine the boiled potatoes, unsalted butter, cream cheese, sour cream, milk, garlic powder, salt, and pepper.
Mash the mixture until smooth and well combined.
Spread half of the mashed potato mixture into a greased baking dish.
Sprinkle half of the shredded cheddar cheese and half of the crumbled bacon over the potatoes.
Repeat the layers with the remaining mashed potatoes, cheddar cheese, and bacon.
Bake in the preheated oven for about 25-30 minutes or until the cheese is melted and bubbly.
Remove from the oven and sprinkle diced green onions on top.
Let it cool slightly before serving.