Preheat the oven to 400 degrees.
Take out the butter, sour cream, and milk and set them aside, they shouldn’t be cold when combined with the potatoes.
Scrub the potatoes clean. Wipe them dry and rub them with canola oil. Place them on a baking sheet and bake for 40 minutes, until they can be easily sliced through.
While the potatoes bake, cook the bacon in a large pan slowly on low heat. As the edges begin to curl, use tongs to flip them over periodically until evenly cooked. Set them aside on a paper towel-lined plate to cool once finished.
Remove the potatoes from the oven and decrease the heat to 350 degrees.
Leave the skins on two of the potatoes and peel and discard the remaining skins. Cut each potato into thirds and add them to a large mixing bowl.
Crumble the cooked bacon and set some aside for topping the casserole. Add the rest to the mixing bowl along with the butter, sour cream, milk, grated cheese, seasoned salt, and salt and pepper.
Smash the potatoes with a potato masher until well-combined and creamy.
Add the potatoes to a greased baking dish. (Mine was 11.25"x7.75" but any size works.)
Top the casserole with reserved bacon and additional shredded cheese.
Bake, uncovered, for 20-25 minutes. Top with sliced green onions and serve!