Tie yoghurt in linen (malmal) cloth till all the water drains out. It might take around 1 hour. It becomes dry creamy texture dough. In a bowl, beat the condensed milk to fluffy mixture for around 10-15 minutes. Add the water drained yoghurt to it and keep beating for another 5 minutes. Prepare your jelly liquid as per the instructions on the packet. Make sure you dont use quick settling jelly otherwise it will become lumps when you'll keep the mousse to set. Now add the jelly liquid when it is at room temperature, to the mixture and beat for another couple of minutes. Pour the mixture in the bowl you want to serve. Keep it in the refrigerator for 2-3 hours or till it sets. Serve topped with fruit jam/sauce of your choice or just plain mousse.