Line a large baking sheet with parchment paper. You may need to use two baking sheets.
Place the pecan halves in groups of three on the baking sheet, making sure to leave a little room between each group.
Add the butter, sweetened condensed milk, corn syrup, and brown sugar to a pot over medium heat. Simmer until the mixture reaches 240 degrees. Stir constantly.
Remove the mixture from the heat and add in the vanilla.
Spoon some of the caramel mixtures over each group of pecans.
Melt the chocolate chips over a double boiler until smooth and creamy.
Spoon some of the chocolate over the caramel on the pecan clusters.
Let the chocolate harden and serve immediately.