Line an 8x8 square pan with non-stick foil.

In a medium-large sized pot, melt chocolate, sweetened condensed milk, cocoa powder, and butter over medium heat until the mixture is completely smooth.

Stir in vanilla extract, salt and chopped nuts (if using)* into the fudge.
Pour the fudge into the prepared pan, smoothing it in an even layer.

Allow the fudge to chill in the fridge for about 4 hours, or until firm.
Remove foil from the pan and cut fudge into squares.

Enjoy!
I would store leftover fudge in the fridge as the fudge does soften when as room temperature