Line an 8-inch square baking dish with parchment paper, leaving some overhang for easy removal.

In a medium saucepan over low heat, combine the chocolate chips, sweetened condensed milk, and salt. Stir continuously until the chocolate is melted and the mixture is smooth.

Remove the saucepan from heat and stir in the vanilla extract. If using, fold in the chopped walnuts and crushed peppermint candies.

Pour the fudge mixture into the prepared baking dish, spreading it evenly.

Refrigerate for at least 2 hours or until the fudge is firm.

Once set, lift the fudge out of the dish using the parchment paper overhang and cut into squares.