While baking pie crust, prepare filling. In a medium sauce pan, mix together filling sugar and cornstarch. Whisk in water. Bring to a light boil on medium heat. Immediately remove from heat. Add half of the mixture to the egg yolks by adding a very small amount at a time and whisking constantly (this will prevent eggs from cooking). Add egg mixture back to sauce pan. Bring back to a boil and stir for 2 minutes, until very thick. (Important to stir for two minutes. If you don’t, the filling will be too thin and won’t hold).