Follow the steps in order for the best result.
Begin by preheating your oven to 400 degrees Fahrenheit. This ensures the casserole bakes evenly and the potato topping gets nice and crispy.
Lightly grease a quiche dish with nonstick cooking spray. This will prevent the potato mixture from sticking to the dish and make serving easier.
In a large mixing bowl, combine the warmed mashed potatoes, sour cream, shredded cheddar cheese, and chopped garlic. Ensure the mashed potatoes are smooth for the best texture.
Season the potato mixture generously with salt and black pepper to your liking. Stir well to incorporate all the ingredients evenly.
Spread the mashed potato mixture evenly into the prepared quiche dish, creating a smooth base for the topping.
Arrange the frozen potato wedges (or crinkle cuts) on top of the mashed potatoes in a spoke wheel fashion. If using curly fries, create a random pattern, breaking any large fries in half to ensure even coverage.
Sprinkle the crumbled bacon, chopped green onions, and grated parmesan cheese evenly over the potato topping. This adds flavor and visual appeal.
Bake in the preheated oven for 25-30 minutes, or until the topping is golden brown and the casserole is heated through.
Remove from the oven and let it cool slightly before cutting into wedges and serving. Enjoy this comforting and flavorful potato casserole!