Let the potatoes cool for 10-20 minutes, or until you can handle them. Slice the potatoes in half the long way, and scoop the flesh of the potatoes into a medium sized mixing bowl, leaving about 1/4 inch of flesh on the potato skins.
Slice the potato halves in half again the short way, making 16 potato skin shells.
In the mixing bowl with the insides of your potatoes, add the butter, sour cream, salt, pepper, shredded cheese, and dijon. Taste for seasoning before adding the egg.
After you add the egg, mix the filling until well combined.