Preheat oven to 400°F.
Pierce the potatoes in several places with a fork.
Place potatoes on middle rack of oven and bake for 45 minutes, or until they are soft all the way through when pierced with a fork. Remove from oven and let cool for 10-15 minutes.
Cut each potato lengthwise and carefully scoop out insides with a spoon.
In a large mixing bowl, blend potatoes, butter and cream with a whisk or hand mixer until light and airy. Mix diced beef with potato mixture, salt, and pepper.
Place filling into each skin halve, and return to the oven for 3-5 minutes.
Top with sour cream, cheddar cheese, or your favorite garnish.