Take a heavy bottomed saucepan. In it, add cocoa, icing sugar, condensed milk and salt. On very low heat, stir continuously, till mixture thickens. Remove from heat.

Add vanilla essence & chopped walnuts and mix nicely.

Take a square pan. Line it with aluminium foil. Spread the mixture evenly into it. Let it cool. When cool, Refrigerate it for 2 hours.