In many tarts and pies using fresh fruit or dried fruit, it was common to make a hole in the lid towards the end of the cooking. A cream custard made from egg and cream was then poured in through this hole and allowed to blend with the fruit and juices for a few minutes as the tart was placed once more in the oven. The result was a delightfully rich and irresistible swirly mix of fruit, juices, custard and pastry. It would almost certainly have been cooked in puff pastry but sweet shortcrust pastry is as nice, I think, and has certain practical advantages.