Combine lemon juice, lemon peel, water, agar flakes and sugar in a small saucepan. Set aside for 10 minutes to soften agar.
Meanwhile, place cornstarch in another small saucepan and gradually stir in cold coconut milk. Bring to a low boil over medium heat, stirring constantly.
Reduce heat to low and continue cooking, stirring constantly, until mixture thickens to a paste-like consistency. Do not overcook.
Remove from heat. Stir in butter and set aside to cool.
Bring agar mixture to a full rolling boil. Reduce heat to medium-low. Simmer for 5 minutes, stirring occasionally. Remove from heat and cool to lukewarm. At this point, agar will have thickened slightly.
When both mixtures have cooled, combine in a blender or food processor. Add lemon extract and food color, blending until smooth.
Pour into cooled, prebaked pie shell. Chill to set.
Garnish as desired.
Serves: One 9-inch pie