In a large pot add sweetened condensed milk, dark brown sugar, salted butter, and corn syrup. Cook over medium to medium-high heat. Stir constantly to avoid burning bottom.
Using a basting brush and water, wash down sided of pot to help sugar to dissolve. (about every minute or so).
Mixture will begin to bubble and increase in volume. Avoid scraping sides of pan as this can make the caramel crystallize during the cooling phase (and go "grainy" or "sugary.") Using a calibrated candy thermometer, cook mixture to 234-238 degrees F or softball stage (depending on how soft or firm you want your caramels to be).
You can also test how soft or firm it is by dipping a spoonful into a cup of ice water to cool quickly.
Remove from heat and add black food coloring (or gel coloring) and anise extract.
Pour into a butter-greased 9x13 inch pan. Pour quickly and DO NOT scrape sides of pan (this can cause the black licorice caramel to crystallize and go grainy.
Once cooled, wrap individual pieces in waxed paper and store in an airtight container or bag. Will keep for several weeks if kept cool.