Preheat oven to 180C/160C fan forced. Lightly grease a 10 x 20cm loaf pan and line with baking paper, allowing the paper to overhang the 2 long sides.
Use electric beaters to beat the sugar, butter and lemon rind in a bowl until pale and creamy. Add the eggs, 1 at a time, beating well after each addition.
Use a large metal spoon to stir the flour and milk, in alternate batches, into the butter mixture until just combined. Stir through the custard powder and lemon juice until combined.
Transfer the mixture to prepared pan and smooth the surface. Bake for 45-50 minutes or until a skewer inserted into the bread comes out clean. Set aside in the pan for 5 minutes before turning, right-side up, onto a wire rack to cool completely.
Slice the lemon bread and serve with extra butter, if using.
