Preheat the oven to 200°C (400°F/Gas 6). Following steps 2–3, roll out and line a 25cm (10inch) fluted loose-based tart tin with the pastry. Blind bake the pastry shell, then remove it from the oven. Reduce the oven to 180°C (350°F/Gas 4).
To make the filling, heat the oil in a frying pan, add the leek and garlic and stir over low heat for 5 minutes, or until the leek is soft.
Meanwhile, roughly chop the rocket leaves. Add the rocket to the pan and stir over low heat for 1 minute. Remove from the heat and allow to cool. Spread the mixture over the base of the pastry shell.
Combine the eggs, milk and cream and whisk until smooth. Pour into the pastry shell. Bake for 30 minutes, or until the filling is set and golden. Serve the quiche topped with the basil leaves and shaved parmesan.