1. Preheat your oven to 425°F or 220°C, making sure it's nice and hot for our dish.

2. Peel the onion and garlic, then chop them into decent-sized pieces. Throw them into a pan with some butter and sauté until the onion is nice and soft.

3. Next, add the ground beef to the pan and cook until it's browned, breaking it up into small pieces as you go. Add some salt and chili flakes to give it a bit of flavor.

4. Now, peel and slice the potatoes into fairly thin rounds. Cut the olives in half and remove the pits. Slice the bell pepper into long, thin strips.

5. In a greased 10-inch or 26 cm round baking dish, create a layer of potatoes. Sprinkle a pinch of salt over them, then add a layer of the beef mixture on top. Next, add a layer of bell pepper, onion, and olives. Repeat this process, finishing with a layer of potatoes on top.

6. Pour the heavy cream over the potatoes, making sure they're all coated. Season with a bit of salt and pepper to taste.

7. Bake the gratin in the preheated oven for about 50 minutes, or until the potatoes are nice and tender. Serve hot, garnished with a few fresh mint leaves if you fancy.