In a heavy saucepan, over medium heat, combine the sugar, brown sugar, corn syrup, butter, salt and condensed milk. With a wooden spoon, stir until the sugar dissolves. Continue to cook, stirring, until smooth and light brown, about 8 minutes. Add the vanilla and pecans and continue to cook, stirring, until the mixture reaches 234 to 240 degrees F. on a candy thermometer or the soft ball stage, that is, when a bit dropped into cold water forms a soft ball that flattens. Remove from the heat and drop by the spoonful onto waxed paper. Let cool. Remove from the paper with a thin knife.