Sprinkle gelatin over cold water; set aside to soften.
Combine 1/2 cup sugar, flour, and salt in a saucepan. Gradually stir in milk. Cook over low heat, stirring until it boils. Boil for 1 minute, and remove from heat. Transfer to a large bowl. Stir in softened gelatin. When partially set, beat with a rotary mixer until smooth. Blend in vanilla and 1 cup coconut.
Whip the cream until stiff. Gently fold into coconut mixture.
In a clean bowl, beat egg whites until frothy. Beat in cream of tartar and 1/2 cup sugar. Continue beating until egg whites form stiff peaks. Fold into coconut mixture. Pile filling into cooled pie shell. Sprinkle with additional coconut. Chill pie for at least 2 hours or overnight.