Combine the sugar, corn syrup, vanilla, & butter in a saucepot and cook over medium heat, stirring, until everything is melted and combined. Whisk in the eggs, one at a time - stirring well after each addition, until all 4 eggs are added. Cook on medium heat for 10-15 minutes, stirring occasionally, until the mixture is lightly browned and thick. Stir in the chopped pecans and cook for an additional 2-3 minutes.