Preheat the oven to 450 degrees F. Place the potatoes on a baking sheet and drizzle with 1 tablespoon of oil. Salt and pepper liberally and shake the pan a little to coat them with oil. Roast for 30 minutes, or until cooked through. Then set aside to cool.
Meanwhile, cook the macaroni in a large pot of salted water, according to package instructions. Drain and set aside in a colander.
Using the same pot, melt the butter over medium-high heat. Once melted whisk in the flour and cook the roux (butter-flour mixture) for 1 minute. Then whisk in the milk and add the sour cream and 8 ounces cream cheese. Bring to a simmer and whisk until the mixture is thick and smooth. Add 1 pound shredded cheddar and whisk until smooth. Then add a dash or two of cayenne pepper and salt and pepper to taste.
Pour the cooked macaroni, 2/3 cup crumbled bacon, and 2/3 cup green onions into the cheese sauce. Stir to coat. Pour the macaroni into a 9x13-inch baking dish and set aside.
For the Potato Skins:
Preheat the oven to Broil. Cut each potato in half lengthwise. carefully scoop of most of the flesh, leaving just a little potato attached to the skin. Reserve the crumbled potato flesh.
Brush the potato skins with oil. With the remaining 2 ounces of cream cheese, place a scant 1/2 tsp dollop of cream cheese in each potato skin.
Sprinkle the crumbled potato over the mac and cheese. Then arrange the potato skins over the top. Sprinkle the remaining 1/4 pound shredded cheddar over the potato skins and add pepper to taste.
For creamy baked mac and cheese, place the baked mac and cheese in the oven under the broiler for 2-3 minutes, watch carefully. You want the cheese to melt and the tops to toast, but not burn. For more a traditional "firm" baked mac and cheese recipe, turn the oven to 400 degrees, and bake for 20 minutes until the tops are golden. Once out of the oven, sprinkle the remaining green onions and bacon over the top and serve warm.