Slice the potatoes into ⅛-inch thick slices. Place the sliced potatoes into water to keep them from oxidizing (turning brown) while you prepare the remaining ingredients.

Preheat the oven to 350°F. Lightly spray a 9x13 baking dish with nonstick cooking spray. Set it aside.

Add the 2 pounds of lean ground beef, diced onions, and garlic to a 4 to 5-quart saucepan (or Dutch oven) over medium-high heat. Stir the ground beef mixture often as it browns, making sure to break up the ground beef as you cook. Drain any excess oil from the pan.

Add the soup, half and half, onion powder, kosher salt, and pepper to a medium-sized mixing bowl. Whisk to combine completely.

Drain the water from the sliced potatoes. Layer ⅓ of the potatoes into the bottom of the prepared baking dish.

Sprinkle ⅓ of the ground beef mixture over the potatoes.

Sprinkle ¾ cup of the shredded cheese over the ground beef layer.

Drizzle ⅓ of the soup mixture over the cheese layer.

Repeat the process for the second layer of potatoes, ground beef, ¾ cup shredded cheese, and soup mixture.

Repeat the potato and ground beef layers, and then drizzle the remaining soup mixture.

Finally, sprinkle the 1½ cups of shredded cheese. Cover tightly with aluminum foil and bake for 1 hour and 10 minutes. Remove the foil and bake for an additional 20 minutes. Allow the casserole to rest for 15 minutes before serving (it will be incredibly hot).