Preheat oven to 350 degrees. Prick holes in the bottom of piecrust. Bake 15 minutes to partially cook.
To make the filling, beat eggnog, eggs, rum (if using), and vanilla in large bowl. Add sugar, salt and nutmeg; mix well. Pour into piecrust.
Bake 25 minutes. Cover with foil and bake 30-40 minutes longer or until a knife inserted in the center comes out clean.
To make the topping, beat whipping cream in a small bowl until soft peaks form. Add confectioners' sugar and rum; beat until stiff peaks form. Garnish pie with whipped cream and sprinkle with nutmeg (optional).