In a small bowl, combine water and cornstarch; set aside.
In a medium saucepan, melt chocolate in sweetened condensed milk over low heat, stirring occasionally. Add cornstarch mixture, eggs, butter, and salt; mix until smooth. Remove from heat and add pecan halves, if desired; mix well and pour into crust.
Bake 30 to 35 minutes, or until a knife inserted in center comes out clean.
Allow to cool on a wire rack then cover and chill at least 2 hours before serving.