heat while stirring until the sugar is dissolved. when the sugar has dissolved, continue cooking and stirring, now on medium heat until the mixture comes to a boil. when it starts boiling, cover and cook for 2 more minutes. uncover and continue cooking (now without stirring) on medium heat until the mixture reaches a temperature of 236 degrees. you will need a candy thermometer for this step.
when it reaches 236 degrees, remove the mixture from the heat and add the vanilla. next add the warmed pecans and stir to coat them with the mixture.
use the remaining 2 tablespoons of butter to grease the pans.
add the coated pecans and place trays 