Roll the pastry out thinly on a lightly floured surface until a little larger than a buttered 28 × 20 cm (11 × 8 inch) fluted loose-bottomed rectangular tart tin. Lift the pastry over a rolling pin, drape into the tin, then press over the base and sides. Trim off the excess pastry with scissors so that it stands a little above the top of the tin. Chill for 15 minutes.
Drain off 1 tablespoon oil from the artichokes into a frying pan, add the onion and garlic and fry for 5 minutes until softened. Scoop out of the pan and reserve. Add the spinach to the pan and fry for 2–3 minutes until just wilted. Tip into a sieve and press out the juices.
Put the tart case on a baking sheet. Arrange the spinach in the base of the pastry case, drain and arrange the artichoke hearts and halved tomatoes on top, then sprinkle with the Parmesan. Beat the eggs and milk with salt and pepper and pour into the tart.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 30–40 minutes until golden brown and the filling is just set. Leave to cool for 15 minutes, then remove the tart from the tin. Cut into squares and serve warm or cold.