Take a bowl and add yoghurt/curd and Powdered Sugar.
Whisk them so well.
Put a lid and keep it aside.
Take a dark chocolate.
Roughly chop the chocolate thinly.
Place a small bowl over the hot water pan (double boiler) and put butter in it.
Let the butter melt.
Then add chopped chocolate.
Mix and let chocolate melt completely. Don't overdo otherwise chocolate will begin to turn dry. However you can do this process (double boiler) in microwave as well.
Immediately drop the melted butter+ chocolate into the bowl having yoghurt sugar mixture.
Give a good mix so that everything incorporates so well.
Put a sieve over the bowl.
Add all purpose flour, cocoa powder, salt and baking soda.
Sift them to the bowl.
Add vanilla essence.
Mix well. The batter of this brownie will be more thick in comparison to the cake batter.
Drop the batter to the 6 inches cake tin lined with greased butter paper.
Bake in pre-heated oven @160°C for 35-40 minutes.
Check by inserting the toothpick and if it comes out clean it's a sign that brownie is well baked.
Let it cool down completely.
Cut and enjoy.