In a large sauce pan, mix 1 cup brown sugar, 1 cup granulated sugar, 1 cup dark corn syrup and 1 cup of the heavy cream. Heat until mixture begins to boil. Slowly stream in the remaining 1 cup of cream into the mixture stirring while boiling. Attach a candy thermometer to the pan and cook over medium heat until 244F. Remove the pan from the heat and add 1/2 cup butter, 2 cups chopped pecans, and 1 tsp vanilla.