Preheat the oven to 400 degrees. Thoroughly wash and dry the potatoes. Wrap the potatoes in aluminum foil and bake for 30 minutes. Remove from the oven. Poke holes in the potatoes and return to the oven for another 30 minutes or until easily pierced with a fork.
Meanwhile, fry and crumble the bacon. Chop the scallions. Remove the potatoes and cool for 10 minutes. Lower the oven temperature to 350 degrees. Slice off the top 1/3 of each potato lengthwise. Holding each potato with a clean towel, hollow out the potato skins with a spoon leaving about 1/4 inch of the potato on the inside to prevent it from falling apart during baking. In a large bowl, combine potato interior, butter, sour cream, 1/2 cup of the Cheddar cheese, heavy cream, milk, salt, and pepper. Mash until smooth. Stir in bacon and scallions.
Fill each potato skin with the mashed potato mixture. Top with the remaining 2 cups of Cheddar cheese. Sprinkle each with chili powder as desired. Bake for 15 minutes or until cheese melts. Top with additional dollops of sour cream, if desired, and serve immediately.