
Preheat the oven to 400 degrees Fahrenheit. Scrub the russet potatoes under running water. Pierce each potato with a knife, and then place on a baking sheet. Drizzle the vegetable oil over the potatoes. Bake in oven for 1 hour. Cool.
Heat a dry frying pan over medium heat and fry the bacon until crispy. Cool before crumbling.
Slice the cooled potatoes in half lengthwise. Use a spoon to scoop out the insides, leaving a little flesh inside the skins. Set the skins aside. Place the scooped-out potato flesh into a bowl and add the butter, sour cream, milk, salt and pepper. Mix well.
Stir in the beaten egg, sharp cheddar cheese, scallions and crumbled bacon.
In a greased baking dish, arrange the potato skins in a single layer. Pour the potato mixture over and around the skins.
Mix the melted butter with the mild cheddar cheese and breadcrumbs. Spread it on top of the casserole.
Bake the casserole, uncovered, for 30 minutes.