Line an 8x8 inch baking pan with parchment paper, leaving some overhang on the sides for easy removal.
In a microwave-safe bowl, combine the white chocolate chips and sweetened condensed milk. Microwave in 30-second intervals, stirring after each, until the chocolate is completely melted and smooth.
Stir in the peppermint extract and green food coloring (if using) until well combined.
Pour the mixture into the prepared baking pan and spread evenly.
If desired, sprinkle the top with chocolate chips and crushed peppermint candies. You can gently press them into the fudge.
Refrigerate for at least 2-3 hours, or until firm.
Once firm, lift the fudge out of the pan using the parchment paper. Cut into small squares.
Notes
Store fudge in an airtight container in the refrigerator.