Heat a pan and add dark chocolate, condensed milk and butter.
Melt mixing altogether.

Stir altogether delicately to prevent air bubbles in the fudge just until the mixture is well combined.
Add chopped cashew nut and walnut and mix well.

Take a box and lined with aluminum foil or parchment paper.
Pour melted chocolate into lined box.

Then cool it in the refrigerator until completely chilled and set.
Then cut the fudge into small squares.