How to Make It
Line bottom and sides of an 8-inch square pan with aluminum foil, allowing 2 to 3 inches to extend over sides; lightly coat foil with cooking spray.
Stir together semisweet chocolate chips, bittersweet chocolate chips, sweetened condensed milk, and butter in a large microwavable bowl. Microwave mixture on HIGH 1 minute; stir. Continue to microwave, stirring every 30 seconds, until mixture is melted and smooth. Stir in vanilla and salt. Pour fudge into prepared pan, and spread in an even layer. Chill 2 hours. Cut fudge into 1-inch squares, and let stand for 30 minutes. Serve at room temperature. Store in an airtight container at room temperature up to 3 days.
Pretzel-Peanut Fudge: Omit bittersweet chocolate chips. Prepare recipe as directed, stirring in 1 cup peanut butter chips with semisweet chocolate chips. Stir in 1/2 cup coarsely crushed pretzels and 1/2 cup coarsely chopped dry-roasted peanuts along with vanilla and salt.
Cherry-Almond Fudge: Omit vanilla. Prepare recipe as directed, stirring in 1 tablespoon cherry liqueur, 1/2 cup coarsely chopped dried cherries, and 1/2 cup coarsely chopped toasted slivered almonds along with salt.
Marshmallow-Pecan Fudge: Prepare recipe as directed, substituting 1 cup (6-oz.) milk chocolate chips for bittersweet chocolate chips. Stir in 1/2 cup coarsely chopped toasted pecans and 1/2 cup miniature marshmallows along with vanilla and salt.