Heat oven to 180C/fan 160C/gas 4. Drizzle half the oil into a small casserole or pie dish and rub all over, then place one steak inside. Scatter over some of the garlic, followed by a layer of onion and tomatoes, then a layer of potatoes on top. Season, then repeat the layers, finishing with the potato.
Drizzle with the remaining oil and then cover the casserole with a tightly fitting lid or cover the pie dish with a double layer of foil. Transfer to the oven for 2 hrs. Remove the lid or foil, turn the oven up to 220C/fan 200C/gas 7 and cook for 30 mins more until the top is golden brown. Serve with some green vegetables.