Instructions

1. Make the crust: In a large bowl, whisk together the flour, powdered sugar, and salt. Add the cold, cubed butter and use a pastry blender or your fingertips to cut the butter into the flour until it resembles coarse breadcrumbs.
2. In a small bowl, whisk the egg yolk and cold water together. Pour this over the flour mixture and mix gently with a fork until the dough just comes together. Form into a disk, wrap in plastic, and chill for at least 30 minutes.
3. Preheat your oven to 190°C (375°F). Roll the chilled dough out on a lightly floured surface to fit a 23cm (9-inch) pie dish. Press the dough into the dish, trim the edges, and prick the bottom with a fork. Chill for another 15 minutes.
4. Line the crust with parchment paper and fill with pie weights or dried beans. Blind bake for 15 minutes. Remove the paper and weights, then bake for another 10-12 minutes, until golden brown. Let it cool completely.
5. Make the filling: In a medium saucepan, whisk together the sugar and cornstarch. In a separate bowl, whisk the egg yolks. Gradually whisk the 350ml of water and the lemon juice into the sugar mixture until smooth.
6. Cook over medium heat, whisking constantly, until the mixture thickens and comes to a boil. Boil for 1 minute. Remove from heat. Temper the eggs by slowly pouring about half of the hot lemon mixture into the yolks while whisking vigorously. Pour the egg mixture back into the saucepan.
7. Return to the heat and cook for 2 more minutes, stirring constantly, until very thick. Remove from heat and stir in the lemon zest and butter until the butter is melted and incorporated. Pour the warm filling into the cooled pie crust. Press plastic wrap directly onto the surface to prevent a skin from forming.
8. Make the Italian meringue: In a small saucepan, combine the 240g of sugar and 80ml of water. Bring to a boil over medium-high heat, stirring until the sugar dissolves. Continue to boil, without stirring, until a candy thermometer reads exactly 118°C (245°F).
9. Meanwhile, when the syrup reaches about 110°C (230°F), start whipping the egg whites and cream of tartar in the clean bowl of a stand mixer on medium speed until they form soft peaks.
10. With the mixer running on low speed, carefully and slowly stream the hot 118°C syrup down the side of the bowl into the egg whites. Once all the syrup is added, increase the speed to high and whip until the meringue is stiff, glossy, and the outside of the bowl is cool to the touch (about 7-10 minutes).
11. Assemble the pie: Remove the plastic wrap from the filling. Immediately spread the meringue over the warm lemon filling, making sure it touches the crust all around to seal it. Create decorative peaks with a spatula.
12. Brown the meringue using a kitchen torch for the best result. Alternatively, place the pie under a preheated broiler for 1-2 minutes, watching it constantly to prevent burning. Chill the pie for at least 4 hours before serving.