Scrub the potatoes well and rinse under cool running water. Pat dry with paper towels and prick the potatoes in several places with a fork. Place the potatoes in the oven and bake for 1 hour to 1 hour and 15 minutes, or until tender. Remove from the oven and set aside on a wire rack until cool enough to handle.
When the potatoes have cooled, cut each potato in half and, using a spoon or a melon baller, scoop the flesh out of the skins, leaving as little flesh as possible. Place the potato flesh in a large bowl and add 1 stick of the butter, the sour cream, heavy cream, salt, and pepper and mash until chunky-smooth. Add the bacon, cubed white Cheddar, half of the grated Cheddar, the green onions, and eggs and mix thoroughly.
Butter a 9 by 13-inch casserole with the remaining tablespoon of butter and reduce the oven temperature to 375 degrees F.
Place the seasoned potato mixture in the prepared casserole and top with the remaining grated Cheddar. Bake for 35 to 40 minutes, or until bubbly around the edges and heated through and the cheese on top is melted and lightly golden. Serve hot.