Boil orange in a pressure cooker (cook in low flame till one whistle) or in a saucepan put 2 cups of water and orange. Boil it for 60 minutes covered in low flame.
After boiling allow orange to cool down completely. Then remove it's pulp and remove pith from the skin.
Wet mixture: In a grinder mix sugar, oil, cold milk, boiled orange (with skin and pulp) and grind into a smooth batter.
Toss cherry with 1 tbsp of whole wheat flour and keep it aside.

Dry mixture: Sieve flour, baking powder, baking soda, vanilla custard powder, salt. Add tossed cherry and keep it aside.
Mix both dry and wet mixtures well.
Put prepared batter into a greased pan and tap the cake pan on a countertop to release any large air bubbles.
Put the cake pan into the preheated pressure cooker and bake it for 1 hour 10 minutes.

Tips:

Use Malta Orange for the best result.
Don’t reduce the quality of sugar otherwise, the cake will taste bitter.
Baking time may vary.
If baking in Oven: Bake in the preheated oven at 180 deg Celsius or around 360 Fahrenheit for about 1 hour 10 minutes. The baking time may vary. So keep checking the cake after 40 - 50

Pressure Cooker Method:
Grease the baking tin with oil and dust it by sprinkling whole wheat flour over greased surface evenly. Pour the mixture into the greased baking tin.

Important Notes:

Use the baking tin of 6 inches in diameter, so that it can easily get into the pressure cooker.
Use a 5-liter pressure cooker. It should be big enough to hold the baking pan.
Baking Tin should be made of Aluminium.

If baking tin comes into direct contact with the base of the pressure cooker, it can burn (overbake) the cake. So use pressure cooker container which has big holes in it or any aluminum small stand.
No gasket and whistle are needed. Remove them before baking.
Don’t add water to the pressure cooker.

How to Bake In A Pressure Cooker?

Heat the pressure cooker on high heat for 2 minutes. Use sea salt or sand as a layer inside a cooker. Put a steel stand on a layer of salt or sand.
Now put the cake tin containing the cake batter (Do not put water inside the pressure cooker).
Close the pressure cooker lid and do not put the whistle on the lid. Remove the gasket (rubber ring) from the lid.
Lower the flame after 2 minutes. Let it bake for 50 -60 minutes on low flame.

After 60 minutes check cake with a knife, if the mixture does not stick, it means the cake is done.
If batter still sticks to knife then again bake for another 10 minutes. Do not open the lid immediately.
Eggless Pressure Cooker Cake is ready.