Boil potatoes in a large pot of water for about 25 minutes or until tender. Drain well and return potatoes to the pot. Mash the potatoes with a potato masher.
Preheat oven to 350 degrees F. Spray a 13×9 inch baking dish with nonstick cooking spray and set aside.
Add sour cream, butter, milk, salt, pepper, bouillon chicken base, garlic salt and garlic powder to the mashed potatoes. Mix well with a mixer or large spoon.
Stir in 1 cup of freshly grated Cheddar Cheese and 2/3 of the crumbled bacon.
Place the potato casserole mixture in an even layer in the prepared baking dish. Bake in oven for 25 minutes.
Remove from oven and evenly sprinkle the top of the casserole with a cup of grated Cheddar Cheese and the remaining crumbled bacon. Return casserole to oven and bake for 5 more minutes, until cheese is melted.
Remove the casserole from the oven. Scatter green onions on top of the casserole and serve.