Step 1 Combine sugar, cornstarch and salt in saucepan. Stir in water gradually. Cook over medium heat, stirring constantly, until mixture thickens. Remove from heat. Whisk egg yolks in medium bowl. Stir small amount of cooked mixture into yolks. Add egg mixture to remaining cooked mixture in saucepan. Bring to boil, stirring constantly. Remove from heat. Stir in lemon juice and butter. Fill baked pie shell with lemon filling.
Step 1 Beat egg whites and lemon juice in large bowl with electric mixer until frothy. Gradually beat in sugar, 1 tbsp (15 mL) at a time, until sugar is dissolved and stiff, glossy peaks form. Spread meringue over filling, sealing to edge of pie shell.
Step 2 Bake in preheated 425°F (220°C) oven until meringue is golden, 4 to 5 minutes.