Preheat oven to 350 degrees F. In a medium bowl stir together crushed crackers, candied pecans, and the melted butter; press onto the bottom and up the sides of a 9-inch pie plate. Bake for 7 to 8 minutes or until firm; set aside. Increase oven temperature to 375 degrees F.
In a medium saucepan combine sugar and cornstarch. Stir in milk, pumpkin, pumpkin pie spice, and salt. Cook and stir over medium-high heat until thickened and bubbly; reduce heat. Cook and stir for 2 minutes more. Remove from heat. In a small bowl lightly beat egg yolks with a fork. Gradually stir about 1 cup of the hot filling into yolks. Add yolk mixture to saucepan. Bring to a gentle boil, stirring constantly; reduce heat. Cook and stir for 2 minutes more. Remove from heat. Stir in the 1 tablespoon butter and the vanilla. Keep filling warm.
Prepare Marshmallow Meringue. Pour warm filling into the prepared pie crust. Spread meringue over warm filling, sealing to edge of crust and swirling meringue into peaks. Bake for 14 to 16 minutes or until meringue is light brown. Cool on a wire rack for 1 hour. Chill for 3 to 6 hours before serving; cover for longer storage.
In a large mixing bowl combine egg whites, cream of tartar, and salt. Beat with an electric mixer on medium-high speed until foamy. Gradually add sugar, 1 tablespoon at a time, beating until soft, glossy peaks form (tips curl). Add marshmallow creme in large spoonfuls while beating at medium speed. Beat until smooth and mixture almost forms stiff peaks (tips stand straight).