Preheat your oven to 375°F. To begin we are going to prepare half of your potatoes for baking. You can use either a baking dish with a lid or wrap your potatoes individually in foil.
Foil Method: tear your foil into pieces that are just large enough to cover your potatoes. Spray each sheet with baking spray, drizzle a little bit of olive oil on each potato as you are wrapping it, and sprinkle the potato with seasoning salt. Poke a hole in your potato so that it does not explode and wrap securely in foil.
Baking Dish: spray your baking dish with baking spray, place your potatoes into the dish, and drizzle with olive oil. Sprinkle with seasoning salt. Cover dish with a lid, or foil.
Place into your oven and bake for at least 1 hour, or until potatoes are baked through completely. You can tell if they are completely cooked by sticking a knife or fork into the center and making sure it goes in easily.
Once your potatoes have been cooked through completely, remove them from the oven and allow for them to cool. Then slice into pieces about ¼ to ½ inch thick.
Cut your remaining half of the potatoes into quarters and place them in a pan. Cover the potatoes in water, and place over medium-high heat until they begin to boil. Allow for potatoes to simmer until they are completely cooked through. You can tell when they are finished by inserting a knife or fork into the potato. If they are soft, then they are finished cooking.
Drain the water from your potatoes and add sour cream. Mash them until the potatoes are smooth. Add shredded cheddar cheese, butter, salt, bacon bits, and pepper to taste. Fold together until your ingredients are mixed. You may also fold in some green onions if desired. Now it is time to assemble your casserole.
In a casserole dish, spray the bottom with baking spray. Then start your first layer, by placing a scoop of mashed potatoes into the bottom and leveling them out. Next, take slices of baked potatoes and place one layer on top of your potatoes. Sprinkle cheese and parsley on top of sliced potatoes.
Next, add mashed potatoes again to create your second layer of mashed potatoes. Then add sliced potatoes. If you have additional ingredients, you may create more layers. When you are finished adding layers, top with shredded cheddar cheese, bacon bits, and some of your green onions.
Bake your assembled casserole at 350°F for 25-30 minutes, just until the edges begin to turn golden. If you would like your cheese a bit crispier, you can try turning your broiler on low for a few minutes, until your cheese is done to your liking. Be sure to keep a close eye on it, if you choose to do this because it can easily burn.
Remove from oven, top with remaining green onions, and serve while hot. Enjoy!