Line an 8x8-inch baking dish with parchment paper, leaving some overhang for easy removal later.
In a medium saucepan over low heat, combine the semi-sweet chocolate chips and sweetened condensed milk. Stir continuously until the mixture is fully melted and smooth.
Remove the saucepan from heat and stir in the vanilla extract and a pinch of salt.
Fold in the crushed peppermint candy canes, chopped walnuts, and mini marshmallows until evenly distributed throughout the fudge mixture.
Pour the fudge mixture into the prepared baking dish and spread it evenly.
Refrigerate for at least 2 hours or until the fudge is firm.
Once set, lift the fudge out of the baking dish using the parchment paper and place it on a cutting board. Cut into squares.
Store the fudge in an airtight container in the refrigerator until ready to serve.
Notes
Arrange the fudge squares on a festive plate and sprinkle some additional crushed candy canes on top for a cheerful look.