Step 1
To make the vanilla custard, stir the custard powder and 125ml (1/2 cup) milk in a medium saucepan until smooth. Stir in sugar and remaining milk and cook, stirring, over medium heat for 5 minutes or until thick. Stir in rind and curd. Set aside to cool slightly.
Step 2
Preheat oven to 180C/160C fan-forced. Grease a 22cm round springform pan. Line base and side with baking paper.
Step 3
Use electric beaters to beat the butter, sugar, vanilla and rind until pale. Add eggs, 1 at a time, beating well after each addition. Fold in the self-raising flour, plain flour and milk until combined. Spoon half the cake mixture into the prepared pan. Smooth surface.