Add whole potatoes with skins to a medium sized pot and cover with cold water, add about a teaspoon salt. Bring water to boil, then cut temperature to simmer and cook until potatoes are tender. Remove from water, cool and cut off the skin. Coarsely grate cooled potatoes into a mixing bowl. Preheat oven to 350°. Spray a 9 x 13 baking dish (or a 2 quart baking dish) with cooking spray. To grated potatoes add sour cream, 1 1/2 cup cheddar cheese, and chopped green onions. Mix well. Place potato mixture into baking dish. Place slices of butter on top, then top with remaining cheddar cheese and crumbled bacon. Cover with aluminum foil and bake about 30 minutes or until bubbly.