Start by mixing cornstarch and brown sugar in a medium saucepan.
In a separate bowl, beat together the egg yolks, water, and a pinch of salt.
Add the egg yolk mixture to the saucepan with the cornstarch mixture. Also, add the chopped pecans.
Place the saucepan on medium heat. Stir constantly until the mixture thickens. Let it boil for 1 minute, making sure to keep stirring.
Take the saucepan off the heat. Stir in the butter until it's fully melted and mixed in. Then, mix in the vanilla extract and pecan halves.
Pour the mixture into a premade pie shell. Make sure it's spread evenly.
Put the pie in the refrigerator. Let it chill for 30 minutes before serving.