Combine cream and milk in a medium saucepan over medium heat and bring to just a simmer.
Meanwhile, whisk yolks, cornflour, vanilla and sugar together in a large heatproof bowl. Gradually whisk in the hot cream mixture until smooth.
Return mixture to cleaned saucepan and place over low heat. Cook, stirring constantly, until custard thickens and thickly coats the back of a spoon.
Serve warm or transfer to a glass bowl and cover surface with plastic wrap (to prevent a skin from forming). Set aside to cool then refrigerate for up to 3 days.
Stir orange zest through the chilled custard.
Layer half the jam roll slices on the base of a 2 litre (8-cup) capacity serving dish, pressing the cut surface of the rolls against the glass. Top with one-third of the custard. Layer three-quarters of the strawberries in the custard, pressing halves against the glass, and scatter with three-quarters of the blueberries. Repeat with another one-third of the custard and remaining jam rolls. Add remaining custard to top of jam rolls.
Top the trifle with dollops of cream. Scatter with raspberries and remaining strawberries and blueberries, pistachios and extra orange zest. Cover and refrigerate until required.