Prune Plum Tart with Custard Filling

A Waie (Waehe in high German) is a classic Swiss tart in which fruit is covered with an uncooked custard cream before it is baked. Prune plums are traditional, and tarts of this type are seen all over Switzerland as soon as the plums come into season in late summer. Apples, poached pears, apricots, rhubarb, and sour cherries also make their appearance in Waien (the plural form) as the seasons progress. Back in the days when people ate more sweets, a Waie was some