Preheat the oven to 375°F (190°C).
Prepare a 2-quart casserole dish with nonstick cooking spray.
Wash the potatoes and pat them dry.
Pierce the potatoes several times with a fork and place them on a baking sheet.
Bake for 45-50 minutes or until tender when pierced with a fork.
Remove and allow them to cool for a few minutes until they are easy to handle.
Slice the cooked potatoes in half and then scoop out the softened flesh, remove it from the skins, and place it in a bowl.
Mash the potato with a mixer, potato masher, or fork.
Add half of the shredded cheddar cheese, sour cream, softened butter, milk, half of the crumbled bacon (if using), half of the sliced green onions, salt, and pepper. Mix well until creamy and thoroughly combined.
Transfer the mixture to the prepared casserole dish, spreading evenly.
Top the casserole with the remaining shredded cheddar cheese and crumbled bacon.
Bake for 20 to 30 minutes or until the casserole is heated through and the cheese has melted.
Once done, remove the casserole from the oven and garnish with the remaining sliced green onions before serving.