Sieve 1 cup whole wheat flour with 1 tbsp custard powder, a pinch of salt, baking powder and baking soda. Keep this sieved mixture aside.
iIn a bowl add the sugar and oil.
Beat this mixture of oil and sugar till well blended and creamy.
Add the orange juice to the sugar and oil mixture. if using whole wheat flour, then 1 cup of orange juice works well and if using all purpose flour, then you can add about ¾ cup of orange juice.
stir very well.
Now add the sieved flour mixture and ½ tsp orange zest.
Mix everything very well. There should be no lumps in the cake batter.
Pour the batter in a lined or greased cake tin of about 7″×4″.
Tap the pan from the sides so that excess air bubbles are released and the batter becomes even in the pan.
Bake in the oven for 180 degrees C for 30-35 minutes.