In a medium saucepan on medium heat, mix together the condensed milk and butter until the butter is melted. Add in the chocolate chips, and mix until the chocolate is melted and remove immediately. Make sure to keep an eye on it! You don’t want your chocolate to burn!
Mix in the salt, peppermint extract and vanilla until fully combined.
Pour the fudge mixture into the prepared pan. Sprinkle the top with the peppermint pieces. Place in the fridge for at least 3 hours before cutting into squares.
Store in an airtight container in the refrigerator.