Sprinkle gelatin over cold water and set aside to soften. Whisk together 1/2 cup plus 1 tablespoon sugar and cornstarch in a small bowl. Whisk in the eggs and add the milk.
Cook in double boiler over simmering water until custard thickens and coats the back of a spoon. Remove from heat. Stir in gelatin until the gelatin melts. Add ice cream while custard is hot. Cool slightly and stir in vanilla.
When the custard is room temperature, whip the cream until medium-stiff peaks form. Fold whipped cream into the custard. Pour filling into pie crust and refrigerate for several hours or overnight, until set.