Preheat your oven to 350 degrees.

Peel the potatoes and cut them into 1-inch cubes. Place the diced potatoes in a large pot and cover with cold water. Bring the water to a boil over high heat. 

Once the water starts boiling, reduce the heat to medium and simmer until your potatoes are fork-tender. This will take about 15-20 minutes. 

While the potatoes cook, fry the bacon in a large skillet over medium-high heat until they become crisp. Transfer the crispy bacon to a paper towel to drain. Crumble the bacon after they cool down. 

Drain the cooked potatoes and transfer them to a large mixing bowl. Add milk, sour cream, cream cheese, butter, salt, pepper, garlic powder, and onion powder to the bowl and mash them with a potato masher or hand mixer. 

Add 2 cups cheddar cheese, crumbled bacon, and sliced green onions to the bowl and fold them into the mashed potato mixture until well combined. 

Transfer the creamy mashed potatoes to a baking dish and spread it evenly using a spatula. Sprinkle the remaining cheese and bacon evenly over the top.

Bake for 30 minutes in your preheated 350 degree oven until the cheese is melted. The internal temperature of the casserole should be about 165 degrees before serving. 

Let the casserole rest for 5-10 minutes before serving. Garnish this easy casserole with sliced green onions or fresh chives.