Spread pecans on a baking sheet and bake until lightly browned. This takes approximately 5-8 minutes. Watch them carefully so they don't burn. Set aside toasted pecans.
In a large heavy sauce pan, combine brown sugar, corn syrup, heavy cream and butter. Bring to a boil over medium heat. Reduce heat to medium low and continue cooking. Stir constantly so it doesn't burn. Cook until mixture is reduced to 3 cups. This takes about 10-15 minutes.
Remove from heat. Stir in bourbon, vanilla and pecans. Let cool.
NOTES: If made in advance, cover and refrigerate up to 2 weeks. To reheat in microwave use 30% power for a minute or two. For the power notation--adjust to your microwave. The goal is to bring this to a room temperature or slightly warm temperature.