In a medium sized sauce pan, put together butter, brown sugar, corn syrup, and salt and bring to a boil. Add sweetened condensed milk, stir constantly to blend.
Boil 15-20 min or so stirring every once in a while (and only stirring on the bottom, don't scrape the sides) until caramel reaches about 235-240 degrees.
Remove from heat and add vanilla. Pour into a greased 9x13 glass baking dish and sprinkle pecans over the top.
Cool for about 30 min, cover with plastic wrap, and then place in refrigerator until ready to roll and dip. When caramel is cooled and easy to handle, cut into 1/2 - 1" squares and roll into balls (should make about 60+ balls)
Break chocolate into pieces and place in a microwave-safe bowl. Melt chocolate in the microwave for 30 seconds at a time at 30-40% power, stirring each time.
Remove caramel balls from fridge and dip in melted chocolate.
Place dipped chocolates on the wax paper and leave at room temperature until chocolate is set. (Do not refrigerate, it will ruin the chocolate).
If you are not eating immediately, place set up chocolates in an airtight container lined with wax paper until ready to serve.