1) Preheat oven to temperature of 355 degrees.
2) Sift flour, icing sugar and custard powder together into a mixing bowl.
3) Rub in butter, using paddle of mixer or by hand, until the mixture resembles breadcrumbs.
4) Add in egg. Mix until the pastry begins to form large lumps. Press together gently with your fingers to form the pastry into a ball.
5) Chill pastry dough for about 30 minutes. In a bowl, mix all ingredients for the filling. Set aside.
6) Divide pastry into 10 portions (approx. 35 g each). Press pastry evenly into tart mould. Trim the edges to remove excessive dough. Prick base of each tart with a fork. Fill tarts with filling to about 90% full.
7) Bake in the preheated oven for 30-35 minutes, until pastry is cooked thoroughly.
8) Leave the tarts in moulds for 5 minutes before turning onto wire rack to cool.
9) Serve the tarts while still warm, or let them cool and then serve.