Preheat oven to 350 degrees F (175 degrees C) and lightly grease a 9x13 inch baking dish.

Boil the 3 lbs of cubed Russet potatoes in a large pot of salted water until tender, about 15 minutes. Drain well.

In a large bowl, mash the hot potatoes with 0.5 cup butter, 1 cup sour cream, and 0.5 cup milk until smooth.

Fold in 1.5 cups of the shredded cheddar cheese, half of the crispy beef pieces (4 oz), 0.5 cup green onions, 1 tsp salt, and 0.5 tsp black pepper.

Spread the potato mixture evenly into the prepared baking dish. Top with the remaining 0.5 cup cheddar cheese and remaining 4 oz crispy beef.

Bake for 20-25 minutes until the cheese is melted and bubbly. Garnish with additional green onions before serving.