Preheat the oven to 220°C/fan 200°C/gas mark 8. Press the pastry into a 23cm round fluted tart tin, allowing it to drape slightly over the edges. Trim the excess and prick the base all over with a fork. Chill in the freezer for 5 minutes.
Line the chilled pastry base with greaseproof paper, then fill with baking beans or rice and bake in the oven for 10 minutes. Remove the paper and beans or rice and return to the oven for another 2 minutes. Remove from the oven and reduce the heat to 200°C/fan 180°C/gas mark 6.
Whisk together the milk and eggs and season. Arrange the cherry tomatoes over the pastry base, then pour over the egg mixture and scatter the cheese and basil leaves. Bake on the middle shelf for 35-40 minutes, until golden brown and set. Cover with a sheet of foil if the top is browning too quickly during cooking.
Meanwhile, put the potatoes in a medium pan and cover with cold water. Bring to the boil and cook for 10-12 minutes until tender. Drain. Cut the quiche into wedges and serve with the salad and potatoes.