Sprinkle gelatin over cold water; set aside to soften.

Combine 1/2 cup sugar, flour, and salt in a medium saucepan. Gradually stir in milk. Cook over low heat, stirring until it boils. Boil for 1 minute, then remove from heat and transfer to a large bowl. Stir in softened gelatin until incorporated. When partially set, beat with a rotary mixer until smooth. Blend in 1 cup coconut and vanilla.

Whip heavy cream in a medium bowl until stiff. Gently fold into coconut mixture.

Beat egg whites in a clean bowl until frothy. Add remaining 1/2 cup sugar and cream of tartar; beat until egg whites form stiff peaks. Fold into coconut mixture.

Pile coconut filling into baked pie crust; sprinkle with 2 tablespoons flaked coconut. Chill in the refrigerator for at least 2 hours or overnight before serving.