Preheat oven to 350˚F (180). Grease and lightly flour cake tin or line with baking paper.
Sift self raising flour and custard powder together.Whisk and combine butter, sugar, orange juice, eggs and orange rind.
Add sifted flour in 2 portions and whisk to combine well.
Pour batter into prepared baking tin and bake for about 30 – 35 mins or until inserted toothpick comes out clean.Cool in pan for about 10 minutes. Put on wire rack to cool completely.
You can substitute with 1 1/4 cups cake flour + 1 1/2 teaspoons baking powder + pinch salt