Prepare your homemade pie crust and chill it in the refrigerator for at least 2 hours before use.

Preheat the oven to 375°F (190°C). Blind bake the pie crust in a 9-inch pie dish using parchment paper and weights or beans to prevent puffing. Bake until golden and set.

Reduce the oven temperature to 350°F (177°C).

In a medium bowl, whisk the 5 egg yolks and set aside.

In a medium saucepan over medium heat, combine the water, 200g sugar, cornstarch, 1/4 teaspoon salt, lemon juice, and lemon zest. Whisk constantly until the mixture thickens, about 3 to 5 minutes.

When the mixture is thick and bubbling, take several spoonfuls of the warm lemon mixture and slowly whisk them into the egg yolks to temper them, so they don’t scramble. Pour this combined mixture back into the saucepan.

Cook for 1 to 2 minutes more, stirring continuously until thickened again. Remove from heat and whisk in the butter until the filling is smooth and glossy.

Pour the hot lemon filling into the warm, baked pie crust.

In a large, clean bowl, beat the egg whites and cream of tartar on medium-high speed until soft peaks form.

Gradually add the remaining sugar and 1/8 teaspoon salt, beating until stiff, glossy peaks form.

Spread the meringue over the warm lemon filling, making sure to seal it all the way to the crust edge to prevent shrinkage. Use a spoon to create decorative swirls.

Place the pie in the oven and bake at 350°F (177°C) for 20-25 minutes, until the meringue is golden brown. If it browns too quickly, tent loosely with foil.

Cool the pie at room temperature for 1 hour, then refrigerate for at least 4 hours before slicing and serving.