Mix vinegar with milk (very lightly warm),so that it curdles a bit.
Mix baking soda,cocoa and flour,add powdered sugar
Add milk and vinegar mix,slowly start mixing all ingredients
Add Oil to the mix and keep on mixing.
transfer the contents to a baking tin.
Garnish with crushed walnuts,bake for at least 30-35 minutes at 170C(fan forced) or until the toothpick comes out clean from the center of the cake
Let it cool on a wire rack,cut into slices