Pre heat oven to 180 degrees centigrade.
Heat the chocolate and butter on a double boiler. Keep aside.
Beat castor sugar, eggs till fluffy, add vanilla essence and mix well.
Gradually add in the melted chocolate mixture to the above batter.
Fold in the flour, cocoa powder and sea salt.
Pour the batter in a tin lined with parchment paper.
Bake at 180 degree centigrade for 30 minutes
Once it is out of the oven and hot, drop nutella and swirl with a tooth pick.
Sprinkle sea salt and keep aside to cool.
