To Make Filling: Combine sour cream, 3/4 cup sugar, cornstarch, yolks and cinnamon in a heavy saucepan; cook until thick, stirring continously. Stir in dates, then remove from heat and let stand for 15 minutes, or until dates are softened. Add vanilla and walnuts to mixture; pour into pie shell.
To Make Meringue: In a large glass or metal mixing bowl, beat egg whites and cream of tartar until foamy. Gradually add remaining sugar, continuing to beat until whites form stiff peaks. Spread meringue over pie, covering completely. Bake in preheated oven for 10 minutes, or until meringue is lightly browned.