
Add potatoes and garlic to a large pot. Fill with water, so the potatoes are completely covered. Bring to a boil, and cook for 15-20 minutes, until the potatoes are fork tender. Drain.
Preheat oven to 350 degrees.
Mash potatoes. Sir in butter, sour cream, and heavy cream. Mash further if necessary to get to your desired consistency. Season with salt and pepper. Stir in 1 1/2 cups cheese, and bacon (reserve some for the topping).
Pour into 13x9 in baking dish. Sprinkle with remaining cheese and reserved bacon. Bake for 20-25 minutes until hot and cheese is melted.
Sprinkle with green onions before serving.