In a saucepan, combine sweetened condensed milk, brown sugar, corn syrup, and remaining butter. Bring to boil over medium heat, stirring occasionally. Reduce heat to maintain a low boil for about 7 minutes, stirring occasionally. Remove from heat and evenly spread 1/3 of the mixture over crackers in pan. Repeat the cracker and caramel layers twice. Immediately sprinkle chocolate chips over the top, allowing to melt approximately 3–5 minutes or until glossy. Spread chocolate over the top.