Heat oven to 425°F. Make pie crust as directed on box for One-Crust Baked Shell as directed on box using 9-inch glass pie plate. Prick crust generously with fork.
Bake 9 to 11 minutes or until golden brown. Reduce oven temperature to 350°F. Cool 5 minutes. Layer pear slices and cranberries in baked crust.
In medium bowl, with wire whisk, beat sugar, nutmeg, sour cream and eggs until smooth and well blended. Pour evenly over fruit.
Bake 15 minutes. Cover edge of crust with strips of foil to prevent excessive browning. Bake 40 to 45 minutes longer or until custard is just set and pears are fork-tender. Cool completely, about 1 hour.
In small saucepan, mix cornstarch with 1 tablespoon of the eggnog until mixture is smooth. With wire whisk, beat in remaining eggnog; cook over medium heat 6 to 8 minutes, stirring constantly, until mixture just begins to boil. Remove from heat; stir in rum. Serve warm sauce over pie. Store pie and sauce in refrigerator.