Preheat your oven to 375°F (190°C). Grease a 9x13-inch baking dish.
Scoop Out Potato Flesh: Cut the baked potatoes in half and scoop out the flesh into a large bowl, leaving about 1/4 inch of potato on the skin. Discard the skins or save for another use.
Make the Casserole Mixture:
Mash Potatoes: Mash the potato flesh until smooth.
Mix Ingredients: Add sour cream, milk, softened butter, 3/4 cup of the shredded cheddar cheese, crumbled bacon, green onions, salt, pepper, and garlic powder to the mashed potatoes. Stir well to combine.
Spread in Baking Dish: Transfer the potato mixture to the prepared baking dish, spreading it out evenly.
Prepare the Potato Chip Crust:
Combine Topping Ingredients: In a bowl, mix together the crushed potato chips, Parmesan cheese, and melted butter until the chips are evenly coated.
Add to Casserole: Sprinkle the potato chip mixture over the top of the potato mixture in the baking dish. Sprinkle the remaining 1/4 cup of cheddar cheese over the top.
Bake:
Bake the Casserole: Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the casserole is heated through and the potato chip crust is golden and crispy.
Serve:
Cool Slightly: Let the casserole cool for a few minutes before serving.
Garnish: Optionally, garnish with additional green onions or crumbled bacon before serving.