Preheat oven to 160 degree C .
Add sugar and yogurt in a bowl and whisk well.
Now add baking powder and baking soda and mix well and then keep aside for 5 minutes (Call it Mixture A)
In a separate bowl, mix refined flour,salt and cocoa powder and sift twice (Call it mixture B).
Mix oil and vanilla essence in mixture A and mix well.
Now gradually add mixture B to mixture A. (Add 2 tbsp at a time and then mix, keep repeating till all the mixture is over)
You may add a few tsp of milk in the mixture, if it becomes too thick.
Pour this mixture in a nonstick cake tin and bake for 45-50 minutes, or check if a tooth pick inserted comes out clean.
Remove from the oven and unmold and then cut into pieces and serve
Let it cool down completely if you want to do icing on it