Wash potatoes thoroughly with a stiff brush under cold running water. Dry with a paper towel. Poke 8−12 deep holes all over the potatoes with a fork. Place potatoes in a bowl and coat with oil. Sprinkle with kosher salt and bake for 1 hour and 15 minutes or until skin feels crisp but flesh beneath feels soft.
While potatoes are baking, heat a skillet over medium-high heat. Brown the ground beef until cooked through, about 7 minutes or until no longer pink. Season to taste with salt and pepper. Drain and set aside.
When potatoes are cool enough to handle but still warm, cut the potatoes in half lengthwise. Cut an oval in each half and scoop out the insides, leaving the skins intact. Mash half of the potato with butter, and then stir in the cream or half and half. Season to taste with salt and pepper. Mix in the ground beef and the blue cheese.
Stuff the mashed potato mixture back into the potato skins. Sprinkle bacon pieces and remaining blue cheese crumbles on top of potatoes. Sprinkle with shredded lettuce and diced tomato, if you wish.