Preheat the Oven: Preheat the oven to 350°F (177°C). Grease a 9x13-inch baking dish with nonstick cooking spray or butter to prevent sticking.
Cook the Ground Beef: In a large skillet over medium-high heat, cook the ground beef, breaking it up with a wooden spoon. Season with black pepper and Cajun seasoning. Cook for 5 to 7 minutes, or until no pink is left. Add the diced onion and minced garlic, sautéing for another 5 minutes until softened and fragrant. If necessary, drain extra fat.
Layer the Potatoes: Line the bottom of the prepared baking dish with an even layer of half of the thinly sliced potatoes. Add a dash of salt and pepper for seasoning.
Add Cheese: Sprinkle ¾ cup of shredded cheddar cheese over the potato layer.
Layer the Beef: Spread the cooked ground beef and onion mixture evenly over the cheese.
Repeat Layers: Add another layer of the remaining potatoes, season with salt and pepper, and top with another ¾ cup of cheese.
Prepare the Sauce: In a medium bowl, whisk together the cream of mushroom soup, cream of potato soup, milk, sour cream, and Worcestershire sauce until smooth. Pour the sauce evenly over the casserole, ensuring it covers all layers.
Bake Covered: Cover the dish tightly with aluminum foil, tenting it slightly to avoid sticking to the cheese. Bake for 1.5 hours, or until the potatoes are fork-tender.
Add Crunchy Topping: Remove the foil and sprinkle the French-fried onions evenly over the top. Place under the broiler for 2–3 minutes until golden brown. To prevent burning, pay close attention.
Rest and Serve: Let the casserole rest for 7–10 minutes before serving. For a splash of color, garnish with chopped parsley or green onions.
