Grease a shallow dish with butter.

Pour the condensed milk into a thick bottomed pan.

Add butter, sugar, cocoa and chopped nuts into the pan.

Stir continuously on a low flame till the mixture leaves the sides of the pan ( about 15 mins ).

Remove from flame and pour evenly into the prepared greased dish.

Allow to cool and set, cut into 1 inch squares.

Store in an air tight tin in the refrigerator.