• Prebake your pie crust before starting your filling. If using a store-bought crust, prebake according to the package instructions. If using a homemade crust, roll the dough into a 12- to 14-inch circle. Place the dough in a 9-inch pie dish, tuck the excess pie dough until, and crimp the edges. Poke the bottom of the crust all over with a fork. Freeze for 20 minutes.
• Preheat the oven to 425°F while freezing. Line the frozen pie shell with foil and fill with pie weights or dried beans. Place on a rimmed baking sheet.
• Bake for 20 minutes. Carefully remove the foil and pie weights and continue baking the crust until golden brown on the edges and the bottom appears dry, about 15 to 20 minutes more. I recommend checking it after 10 minutes in case your oven or pie pan bakes faster. (If the edges are taking on too much color, wrap with a pie shield or aluminum foil to prevent from burning.) Remove and let cool completely.

For the Filling:

• In a medium mixing bowl, whisk the egg yolks until smooth and set aside.
• In a medium pot, whisk together the sugar, cornstarch, and salt. Add the lemon zest, then slowly whisk in the water and lemon juice until the cornstarch is dissolved. Place over medium heat and whisk frequently until thickened and starting to bubble, about 5 minutes. Remove from the heat.
• Temper the egg yolks by slowly pouring about 1 cup of the hot lemon mixture into the egg yolks while whisking. Slowly pour the tempered egg yolk mixture into the pot while whisking. Place over medium-high heat. Continue whisking until the mixture is thickened enough for the whisk to leave a defined trace and the mixture starts to bubble, about 2 minutes.
• Remove from the heat and whisk in the butter until fully melted and combined. Pour into the baked pie shell. Chill for at least 4 hours or up to 24 hours before topping and serving (press plastic wrap to the surface if chilling it overnight to serve the next day).

For the Meringue:

• When you are ready to top and serve the pie, preheat the oven to 350°F.
• Combine the egg whites and cream of tartar in the mixing bowl of a stand mixer fitting with a whisk attachment. Beat on medium-high speed until frothy. Slowly add in the sugar. Continue beating until stiff, glossy peaks form, about 5 minutes. (The meringue should also feel completely smooth when you rub a small amount between your fingers. If it feels gritty at all, beat it for another minute to finish dissolving the sugar, and check again.)
• Spread the meringue over the top of the lemon filling, making sure it goes all the way to the edge and touches the crust.
• Bake for 15 to 20 minutes or until the meringue starts to turn golden brown. Serve immediately, or chill for up to 4 hours before serving.