These fritters need to be served straightaway, while the custard is warm and oozy. They're a self-contained fruit and custard parcel - all that's needed to finish them is a light dusting of icing sugar.
For deep-frying:vegetable oil180 gmplain flour2 tspcaster sugar2eggs, separated180 mlbeer, at room temperature (lager or wheat beer ideally)60 gmunsalted butter, melted4medium plums, halved and stones removedTo serve:icing sugarVanilla custard600 mlmilk1vanilla bean, split lengthways140 gmcaster sugar120 gmplain flour60 gmbutter, diced90 gmegg yolk (about 5 yolks)
For vanilla custard, bring milk, vanilla bean and 40gm of sugar to the boil in a saucepan over medium-high heat. Place flour, butter and remaining sugar in a bowl and, using fingertips, rub mixture together until it resembles coarse breadcrumbs. Whisk in milk mixture until smooth, return to pan and continue stirring mixture over low-medium heat until thick and flour cooks out (5-6 minutes). Remove from heat, discard vanilla bean, then whisk in yolks, cover directly with plastic wrap and refrigerate until cold.
Heat vegetable oil in a large deep saucepan or deep-fryer to 170C. In a large bowl combine flour and sugar, make a well in centre, add yolks and beer and whisk to combine, then stir in butter. In a separate bowl whisk eggwhites to soft peaks and gently fold into batter.
Mould custard around each plum half, dip into batter and deep-fry in batches, turning occasionally, until golden brown (3-4 minutes; be careful, hot oil will spit). Drain on absorbent paper and serve hot dusted with icing sugar.