Sieve flour,sugar, Cocoa powder,salt and baking powder and keep aside.
In a bowl beat yogurt and oil,add vanilla essence
Fold in the flour mix until just Incorporated.
Fold int the chopped walnuts
Pour the batter in a greased pan and bake in a preheated oven at 180 degree Celsius for 30-35 minutes.
Let cool,then demould and cut into pieces