Preheat oven to 375. Wash potatoes thoroughly, and pat dry. Poke several holes for steam to escape. Bake until done (about 45 minutes). You want the potatoes done, but not to the point where the skin is pulling away from the potato. Remove from oven and allow to cool.
Split potatoes lengthwise and scoop out insides into a mixing bowl, leaving a small border of potato next to the skins.
Mash potatoes with enough half and half to moisten. Add cheddar, bleu cheese, and crumbled bacon. Mix thoroughly. Chop green onions and tops. Add to potato cheese mixture.
Fill each potato skin just slightly above the top. Sprinkle with extra sharp cheddar cheese. Grate Parmesano Reggiano on top of cheddar.