Preheat oven to 365°F and set an oven rack in the middle position.

Grab 4 eggs and separate the egg yolks from the egg whites and set aside.

4 large egg yolks

[Note: to save yourself some time, we recommend using a store-bought pie crust]

In a medium bowl, mix together the graham cracker crumbs and sugar. Add the melted butter; stir with a fork first, and then your hands until the mixture is well combined.

[Note: try greasing the pie pan before the next step]

Using your fingers and the bottom of a clean drinking glass or measuring cup, press the crumbs firmly into the bottom and up the sides of a 9 x 1.5-inch pie pan. The crust should be about ¼ inch thick.

12 graham crackers

6 tbsp salted butter

1/3 cup granulated sugar

Bake for 10-15 minutes, until just slightly browned. Let the crust sit on a wire rack while you prepared the rest of the pie.

1 egg

In a medium saucepan (away from any heat), whisk together 1 cup sugar, flour, cornstarch, and salt.

Note: try using less water for the next step. We're just going to reduce/evaporate most of it anyway.

Stir in water, lemon juice and lemon zest. Cook over medium-high heat, stirring frequently, until mixture comes to a boil. Remove from heat and stir in butter. 

1 cup granulated sugar

2 tbsp all-purpose flour

4 tbsp cornstarch

1/4 tsp salt

1 cup water

1/2 cups lemon juice

1 tbsp lemon zest

3 tbsp unsalted butter

Beat the egg yolks with a fork. Add a spoonful of the hot saucepan mixture into the egg yolk mixture and whisk together to temper the eggs (gradually warm them).  Repeat, with a few more spoonfuls. Whisk the egg yolk mixture back into remaining sugar mixture in the pot. 

4 large egg yolks

Bring to a gently boil and continue to cook while stirring constantly, until thick.

Note: if the mixture does not appear to be thickening to your desired amount, proceed to the next step at around the 8-10 minute mark.

Remove lemon filling mixture from heat.

Bonus/optional: strain through a mesh strainer into a heat-safe bowl. This will remove the zest and any other bits that may have thickened slightly faster than the overall mixture, resulting in a more even texture and consistent flavor profile throughout the entire pie.

Add mixture to a heat-safe bowl. Let sit at room temperature while you begin your meringue.

Prepare a double boiler. We use a medium-to-large sized ceramic bowl and a medium-sized saucepan that is large enough (or... small enough) to suspend the bowl without it touching the bottom of the pan. Make sure that the bowl is completely clean, dry, and grease-free.

Without turning on the heat yet, in the bowl of the double boiler, whisk together sugar, cream of tartar, and salt.

2/3 cup granulated sugar

3/4 tsp cream of tartar

1/8 tsp salt

Add egg whites and whisk until completely combined.

5 large egg whites

Fill the bottom of the double boiler with about 1 ½ inches of water and bring to a simmer over medium-low heat. Rest the bowl of your mixer over the simmering water (it should not be touching the water).

Whisk mixture constantly until the mixture reaches 160F (70C) and the sugar is dissolved. You can test this by carefully (it’s hot!) rubbing a small bit between your fingers, it should be smooth and not gritty (if you've been whisking fairly constantly, it's very unlikely to still be gritty).

Remove mixing bowl from heat and dry the bottom of your bowl.

Note #1: if you used a different bowl from the one that you'll be using for mixing, run the outside of that bowl under warm water to make it warm (not hot). Make sure the inside of the bowl remains dry.

Add the lemon mixture back into the (cleaned) saucepan to begin reheating on low/simmer. The lemon mixture will have thickened a bit more due to cooling, but will become somewhat more thin when reintroduced to heat.

Fit bowl into your stand mixer (if using a stand mixer, otherwise use an electric hand mixer for the next step).

Use the whisk attachment on medium-high speed to beat the egg white mixture to stiff peaks. Add vanilla extract after about 2 minutes. Continue beating for an additional 3 minutes. Meringue should be thick, billowy, and glossy. This typically takes around 5 minutes total (using level 6 on a KitchenAid mixer).

1/2 tsp vanilla extract

Add the simmering lemon filling mixture to your pie crust. Immediately after, gently scoop meringue over pie filling. Use your spatula or the back of a spoon to create peaks from the meringue. Place on a baking sheet and transfer to the 2nd from bottom rack of 375F (190C) oven for ~14 minutes, until peaks of meringue are browning and the meringue appears relatively stiff (not jiggly) if gently shaken. Note: 11 minutes was all we could do at 375; the meringue started to get a little too dark. We may want to keep the oven at 365 (or even 350) to allow for longer cooking - which should ensure that the meringue is completely done without overcooking - but we'll taste and decide.

Allow pie to cool at room temperature for at least an hour before slicing. If you prefer a thicker lemon filling or meringue, after the hour has passed, transfer to the refrigerator to cool completely (about 4 hours) before slicing and serving. This pie is best served the day it is made or next day.