To Make Pineapple Layer: In a medium saucepan combine 1/3 cup sugar, cornstarch, and pineapple with juice. Cook over low heat, stirring occasionally, until mixture is the consistency of jelly.
To Make Cream Cheese Layer: In a medium mixing bowl, whip cream cheese until fluffy. Whip in sugar and salt until mixture is smooth. Add eggs, vanilla, and milk. Beat mixture until all ingredients are thoroughly combined. Mixture will be liquidy.
Pour half of pineapple mixture into each pastry shell. Pour half of cream cheese mixture over each pineapple layer. Sprinkle with chopped walnuts if desired.
Bake in preheated oven for 10 minutes. Reduce heat to 325 degrees F (165 degrees C) and bake an additional 50 minutes, until tops of pies begin to brown. Chill before serving. Top with whipped cream if desired.