1. Prepare 9-inch baked pie shell as directed; cool.
2. Meanwhile, in heavy 1-quart saucepan, beat milk, salt, egg yolks, and 1/4 cup sugar until well mixed. Sprinkle gelatin evenly over mixture; let stand 1 minute to soften gelatin slightly. Cook over medium-low heat, stirring constantly, until mixture thickens and coats a spoon (do not boil or mixture will curdle). Remove saucepan from heat; stir in vanilla. Refrigerate gelatin mixture, stirring occasionally, until mixture mounds slightly when dropped from a spoon, about 40 minutes.
3. In large bowl, with mixer at high speed, beat egg whites until soft peaks form; gradually sprinkle in 1/4 cup sugar, beating until sugar completely dissolves and whites stand in stiff peaks.
4. In small bowl, using same beaters, with mixer at medium speed, beat heavy cream until stiff peaks form. With rubber spatula or wire whisk, gently fold whipped cream and gelatin mixture into egg whites. Spoon mixture into pie shell; sprinkle filling with ground nutmeg. Refrigerate pie about 3 hours or until filling is set.