Preheat oven to 375°F. Grease a 9×13 inch baking dish with butter or cooking spray. Peel and slice potatoes into ⅛-inch thin rounds using a mandoline or sharp knife. Dice onion into small pieces. Grate cheese if using a block. Set everything aside for easy layering.

In a medium bowl, crumble the ground beef and season it with 1 teaspoon salt, ½ teaspoon black pepper, and ½ teaspoon garlic powder. Mix well with your hands to distribute seasoning evenly throughout the beef. This ensures every bite has flavor.

Start with half the sliced potatoes arranged in an even layer on the bottom of the greased baking dish. Sprinkle with ½ teaspoon salt, ¼ teaspoon pepper, and ¼ teaspoon garlic powder. Add half the diced onions spread evenly over potatoes. Crumble half the seasoned ground beef over the onion layer, breaking it into small pieces. Sprinkle 1½ cups shredded cheese over the beef.

Create a second layer using the remaining ingredients in the same order: potatoes, seasoning (remaining salt, pepper, garlic powder), onions, ground beef, and cheese. Press down gently with your hands to compact the layers and help everything cook evenly.

Pour the beef broth slowly around the edges of the casserole dish—not directly over the top layer. This keeps the cheese from getting soggy while adding moisture for tender potatoes. Dot the top with small pieces of butter for extra richness and golden color.

Cover the baking dish tightly with aluminum foil, making sure it's sealed around the edges to trap steam. This is crucial for cooking the potatoes through without drying out the beef. The steam created inside will make everything tender.

Place covered casserole on the middle oven rack and bake at 375°F for 45 minutes without opening the oven. The potatoes need this time to steam and become tender. Don't peek or you'll release the steam that's cooking everything.

After 45 minutes, carefully remove the foil (watch for hot steam). Return casserole to oven uncovered and bake another 15-20 minutes until the cheese on top is bubbly, golden brown, and slightly crispy around the edges. Potatoes should be fork-tender when pierced.

Insert a fork into the center of the casserole—it should slide through the potatoes easily with no resistance. The beef should be fully cooked through with no pink remaining. If potatoes aren't tender yet, cover and bake another 10 minutes.

Remove casserole from oven and let it rest for 5 minutes before serving. This allows the layers to set up so portions hold together better when scooped. The cheese will also thicken slightly as it cools just a bit.

Use a large serving spoon to scoop generous portions, making sure to get through all the layers in each serving. Garnish with fresh parsley if desired. Serve hot and enjoy this ultimate comfort food casserole with your favorite sides.