In a medium saucepan, stir together sugar and cornstarch. Add boiling water, stirring well. Cook over direct heat, stirring constantly, until thick and clear. Stir in rind and lemon juice. Continue cooking and stirring until mixture comes to a boil. Remove from heat.
In a small bowl, beat eggs yolks. Gradually add half of hot lemon mixture, stirring constantly. Pour egg mixture into saucepan. Cook, stirring, for 1 minute. Remove from heat. Stir in butter until melted. Cool.
In a small bowl, beat egg whites with lemon juice until soft peaks form. Gradually beat in sugar, a spoonful at a time. Continue beating until meringue is stiff and glossy.
Pour cooled filling into baked pie shell. Pile meringue over filling, being sure it meets the crust all around to prevent shrinking or weeping. Swirl meringue with back of spoon to form peaks. Sprinkle coconut on meringue. Bake 10 to 15 minutes, or until meringue is delicately browned.
Cool at least an hour before serving. Store in refrigerator.
In a 4 cup (1 L) microwaveable bowl, combine sugar and cornstarch. Gradually stir in water. Cook in microwave on ‘High’ (100%) 4 minutes or until mixture comes to a boil and thickens, stirring after 2 minutes.
In a bowl, beat egg yolks. Whisk about a third of hot mixture into egg yolks; add egg yolk mixture to remaining hot mixture and blend well. Cook in microwave on ‘High’ (100%) 1 minute or until thickened. Stir in butter, lemon rind and juice. Pour into baked pie shell.
Beat egg whites with lemon juice until frothy. Gradually beat in sugar until mixture forms stiff peaks. Spread over hot filling. Cook in microwave on ‘Medium High’ (70%) 3 to 4 minutes, or until set.
Spread coconut in a shallow microwaveable dish. Cook in microwave on ‘Medium High’ (70%) 3 to 4 minutes or until lightly browned, stirring several times. Cool. Sprinkle coconut on meringue.