Bake your pie crust according to the directions on the package.  

Preheat oven to 350 degrees.

In a sauce pan, combine the dark syrup and brown sugar.  Boil over a medium heat continuously stirring until the sugar crystals have dissolved.  

In a medium bowl, beat the eggs and then add the 1/4 cup of melted butter 

Add the syrup and sugar mixture to the eggs and butter.  Be careful not to add the syrup mixture until it's cooled down a bit.  If it is too hot it will begin to cook the eggs.  Mix it all together until well combined.  

Add 1 1/2 cups of the pecan halves and then add the vanilla extract and mix together until well combined.  

Pour the mixture into the pie shell.

Arrange the remaining pecan halves on the top of the pie.  

Bake the pie at 350 degrees for 50-60 minutes.  You can tell when it's done when the center doesn't jiggle when you lightly shake the pie back and forth.  Check the pie at about 30 minutes and if it's browning too fast cover it with aluminum foil.