Add the corn syrup and brown sugar, and stir until the sugar has melted.
Pour in the condensed milk, and stirring constantly, cook until it's starts to thicken and small bubbles are forming on the side of the pan. If you're using a candy thermometer, cook to 220 degrees.
Take off heat, and stir in vanilla. Let it cool for a few minutes before dipping.
Notes
*Makes about 2.5 cups. You can refrigerate it for about a week.