1. Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with butter or olive oil.
2. In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until they become translucent and fragrant, about 3-4 minutes.
3. Add the ground beef to the skillet, breaking it apart with a wooden spoon. Cook until the beef is browned, approximately 6-8 minutes. Drain any excess fat.
4. Season the beef with salt, pepper, paprika, and thyme. Stir well to combine all the flavors.
5. In the prepared baking dish, layer half of the sliced potatoes, followed by half of the beef mixture. Repeat with the remaining potatoes and beef.
6. In a small saucepan, melt the butter over low heat. Stir in the milk and bring to a gentle simmer. Pour this mixture evenly over the casserole.
7. Top the casserole with shredded cheddar cheese, ensuring even coverage for a beautiful golden crust.
8. Cover the dish with aluminum foil and bake in the preheated oven for 45 minutes. Remove the foil and bake for an additional 15 minutes, or until the potatoes are tender and the cheese is bubbly and golden.
9. Allow the casserole to cool for 5-10 minutes before serving. This will help the layers set and make it easier to serve.

Chef Sofia’s Tip: For a crispier top, you can broil the casserole for the last 2-3 minutes, watching carefully to prevent burning.