Heat the oven to 200C/180C fan/gas 6 and oil a 22cm pie dish. Cook the potatoes in a large pan of boiling salted water over a high heat until just tender, about 12-15 mins. Once the potatoes are cooked, drain, then tip into the pie dish and roughly break up using a potato masher until they cover the base of the dish and up the side, forming a crust. Brush over more oil, then bake for 10-15 mins until beginning to turn golden.

Meanwhile, heat the 1/2 tbsp oil in a large frying pan over a medium heat and brown the meatballs all over. Remove to a plate using a slotted spoon. Fry the onion and carrot in the leftover oil in the pan over a low heat for 8-10 mins until softened.

Tip in the cherry tomatoes and garlic, and fry for 5-10 mins more until the tomatoes have broken down. Add the tomato purée and passata, cook for 5 mins until thickened slightly, then return the meatballs to the pan. Tip the meatball mixture into the pie dish over the potato base. Scatter over the cheese, then bake for 30-40 mins until the cheese is golden. Scatter over the basil leaves before serving.