Cake flour is not plain flour or self-raising flour. Cake flour is a low protein type of flour.
If you cannot find cake flour, then for every 120g of plain flour, remove 2 tbsp of it and replace with 2 tbsp cornstarch to achieve the effect of cake flour.
If you cannot find cake flour, then for every 120g of plain flour, remove 2 tbsp of it and replace with 2 tbsp cornstarch to achieve the effect of cake flour.