Grease 8x8 inch baking pan. Optional: line the bottom of the pan with parchment paper for easy removal.
In a medium saucepan, warm chocolate chips, butter and sweetened condensed milk together. Stir over low heat until chocolate is completely melted.
Remove from heat and stir in vanilla extract.
Pour into prepared pan and sprinkle peppermint chips on top. Chill in refrigerator for a few hours or until firm.