1. Preheat your oven to 375°F (190°C). This is a sweet spot that lets the potatoes cook through while the casserole crisps up on top.
2. Heat olive oil or butter in a large skillet over medium heat. Add the chopped onion and garlic, cooking until softened and fragrant—about 3 minutes. This base layer of flavor is where the magic starts.
3. Add the ground beef to the skillet. Break it up with a spoon and cook until browned and no longer pink. Drain excess fat if necessary to keep things from getting greasy.
4. Stir in the dried thyme or Italian seasoning, salt, and pepper. I like to taste a little here because seasoning can make or break the whole dish.
5. In a separate bowl, whisk together the cream of mushroom soup and milk until smooth. This will be your creamy binder that brings everything together.
6. Lightly grease a 9×13-inch baking dish. Spread half of the sliced potatoes evenly on the bottom. Pro tip: thin slices cook faster and more evenly, which means no waiting forever for potatoes to soften.
7. Layer half of the cooked ground beef mixture over the potatoes, then pour half of the soup mixture on top. Repeat with the remaining potatoes, beef, and soup mixture.
8. Sprinkle the shredded cheese evenly over the top. This is the part where your kitchen starts smelling irresistible.
9. Cover the dish with foil and bake for 45 minutes. Then, remove the foil and bake for an additional 15 minutes until the cheese is bubbly and golden brown.
10. Let the casserole rest for about 10 minutes before serving. This makes it easier to slice and helps all those flavors settle in.

When I first made this for my family, I remember how the kids practically fought over the cheesy edges. That bubbly, golden top is a reward for all the waiting—and trust me, it’s worth every second.