Preheat your oven to 350°F (175°C). Roll out and fit the pie crust into a pie dish, crimping the edges and pricking the bottom to prevent bubbling. Bake for 10-15 minutes until lightly golden, then cool completely.

In a saucepan, combine freshly squeezed lemon juice, egg yolks, granulated sugar, and cornstarch. Whisk until smooth, then cook over medium heat, stirring constantly until thickened (about 7-10 minutes). Remove from heat and stir in butter until melted.

In a clean bowl, beat egg whites with cream of tartar until soft peaks form. Gradually add superfine sugar and continue to whip until glossy and stiff peaks form.

Pour the lemon filling into the cooled pie crust. Spread the whipped meringue over the filling, sealing the edges and creating peaks. Bake for 10-12 minutes until the meringue is light golden brown.

Once baked, cool the pie at room temperature for about 2 hours, then chill in the refrigerator for an hour before serving.