Preheat the Oven:

Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish and set aside.

Cook the Potatoes:

Place the cubed potatoes in a large pot of salted water. Bring to a boil and cook until the potatoes are fork-tender, about 15-20 minutes. Drain the water and return the potatoes to the pot.

Mash the Potatoes:

Using a potato masher or fork, mash the potatoes until smooth. Add the sour cream, milk, butter, garlic powder, salt, and pepper. Stir until well combined.

Add Mix-Ins:

Fold in 1½ cups of cheddar cheese, most of the bacon, and most of the green onions. Mix until evenly distributed.

Assemble the Casserole:

Transfer the potato mixture to the prepared baking dish. Spread it out evenly and sprinkle the remaining ½ cup of cheddar cheese over the top. Cover with aluminum foil.

Bake:

Bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.

Garnish and Serve:

Remove the casserole from the oven and sprinkle with the reserved bacon and green onions. Serve hot and enjoy!