Dissolve cornstarch with 3/4 cup of water in a bowl.

Beat egg yolks and stir into the cornstarch mixture; set aside.

In a saucepan, melt 3/4 cup of sugar over low to medium heat until golden brown.

Add the remaining 3/4 cup sugar, 1/2 cup butter, and the remaining 3/4 cup water to the saucepan.

Bring the mixture to a boil, stirring until the butter has melted and the sugar has dissolved completely.

Stir the cornstarch and egg mixture into the saucepan and bring the mixture to a low boil, stirring constantly.

Continue to boil slowly until the mixture thickens.

Remove the mixture from the heat and stir until smooth.

Let the mixture cool.

Stir in the vanilla.

Pour the filling into a baked pie crust.