Line 2 baking sheets with parchment paper. Arrange pecan halves clusters of 4 in an "X" shape on a parchment-lined baking sheet (see photos).
In a heavy bottomed saucepan, bring the butter, brown sugar, and corn syrup to a boil over medium heat. Add the sweetened condensed milk, vanilla, and salt. Insert your candy thermometer and continue cooking and stirring until the mixture reaches 245℉.
Working quickly, spoon about a tablespoon of the caramel on each pecan cluster, connecting the 4 pecans together.
Allow them to sit at room temperature for 15 minutes, or until caramel has set.
In a microwave safe bowl, melt the chocolate as directed on the package or in 20 second increments, stirring after each, until melted and smooth.
Working quickly, spoon a bit of the melted chocolate on top of the caramel on each candy. Allow the chocolate to set before storing or serving.
Notes
How to toast pecans:
In the Oven: Bake pecans on a sheet pan in an even layer for 8-10 mins at 350℉.
On the Stovetop: Heat for 3-5 minutes on the stovetop, stirring often.
Allow toasted pecans cool to room temp before handling.
Storage: Store pecan clusters in airtight container with parchment paper between layers for up to 2 weeks, in the fridge for up to 3 weeks, or freeze for up to 3 months (thaw at room temperature about 60 mins).