Preheat oven to 350 degrees. In a large sauce pan we are going to create a bechamel sauce. Let's begin by melting the butter fully. Before proceeding with the bechamel, add the diced onion and diced pancetta and allow to brown. Then stir in the flour, salt, and pepper until the mixture is smooth.  

Gradually add the cream and allow to begin to boil while stirring well. Remove from the heat, stir in the garlic powder and the cheese until melted. 

Lightly grease a separate oven safe bowl. Place a layer of scalloped potatoes. Pour some of the cheese mixture over the potatoes. Add another layer of scalloped potatoes and cheese mixture. Repeat until you have used all of the potatoes and cheese sauce.

Cover and bake for one hour. Then remove the cover and bake for an additional 45 minutes or until the potatoes are tender. Remove from the oven and top with a pinch of salt, pepper, and the chopped green onions. Serve with sour cream while piping hot and melty!