Combine first 5 ingredients in a heavy saucepan. Cook over medium heat, stirring constantly, until mixture comes to a boil. Boil 6 minutes, stirring constantly. Remove from heat; pour half of mixture into a small bowl.
Add bittersweet chips to half of marshmallow mixture, stirring until chips melt. Stir in extract. Spread mixture into a buttered 8-inch square pan.
Stir white chips into remaining half of marshmallow mixture, stirring until chips melt. Pour mixture over chocolate layer in pan. Sprinkle chopped candies over white chocolate layer. Cover and chill 1 hour or until firm. Cut into squares.
Recipe by Kitchen Meets Girl at https://kitchenmeetsgirl.com/black-and-white-peppermint-fudge/