Peel and halve the potatoes. Boil in salted water until soft. Mash with butter and milk until smooth and creamy. Set aside.

Heat olive oil in a pan. Sauté onion and garlic until golden and fragrant.

Add ground beef. Season with salt and pepper. Cook until browned and liquid evaporates. Stir in chives.

Grease a baking dish. Layer half the mashed potatoes, top with half the cheese, and spread the sautéed beef over it.

Cover with the remaining mashed potatoes and sprinkle the rest of the cheese on top.

Bake at 180°C (350°F) for 40 minutes, or until the cheese is golden and bubbly. Let cool slightly, sprinkle some chopped thyme (optional) before serving.