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), vanilla custard powder and grind into a smooth batter.

Toss soaked dried red cranberries and chopped dried apricot with 1 tbsp of whole wheat flour. Keep them aside.
Dry mixture: Sieve flour, baking powder, baking soda or Eno, salt. Add tossed cherry and keep it aside.
Mix tossed dried red cranberries, chopped dried apricot with dry and wet mixtures. Mix them well.

Put prepared batter into a greased pan and tab the cake pan on a countertop to release any large air bubbles.
Put cake pan into the preheated pressure cooker and bake it for 1 hour 10 minutes.

Tips :

Soaked dried red cranberries in a half cup water for half an hour. Remove water and dry it completely. Then add into the flour mixture. By soaking it will slice easily.
For best results use orange with thin skin.
“Malta” orange is perfect for this cake.
You can use 1 cup of whole wheat flour too.
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 to 45 minutes.

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.