1. Preheat your oven to 375°F (190°C).

2. Heat the oil in a large pan over medium heat.

3. Add the onion and cook until softened, about 5 minutes.

4. Add the garlic and cook for 1 minute.

5. Add the ground meat, breaking it up with a spoon as it cooks, until it's no longer pink.

6. Stir in the crushed tomatoes, tomato paste, salt, and pepper.

7. Bring the mixture to a simmer and let cook for 10-15 minutes, stirring occasionally.

8. In a large baking dish, spread half of the prepared potato gratin.

9. Top with the meat mixture, followed by the remaining potato gratin.

10. Sprinkle the grated cheese over the top.

11. Transfer the dish to the preheated oven and bake for 25-30 minutes, or until the top is golden brown and the gratin is heated through.

12. Serve hot and enjoy!