For the crust:
- 1 1/3 cups graham cracker crumbs (from 1 sleeve, or 9 large crackers)
- 2 tablespoons sugar
- 5 tablespoons unsalted butter, melted

For the filling:
- 1 cup sugar
- 1/3 cup cornstarch
- 1/4 teaspoon salt
- 1 1/2 cups water
- 1/2 cup fresh lemon juice
- 5 large egg yolks, at room temperature
- 2 tablespoons unsalted butter, at room temperature, cut into pieces
- Grated zest from 1 lemon (about 1 1/2 tablespoons)
- 1/2 teaspoon vanilla extract (optional)

For the meringue:
- 3 large egg whites at room temperature
- 1/4 teaspoon cream of tartar
 6 tablespoons sugar

To make the crust:

1. Break up the graham crackers and place in a food processor. Process the crackers with the sugar for about 20 seconds, or until the crackers become fine crumbs.

2. Add the melted butter and pulse about 10 times, just until incorporated. (If you do not have a food processor, you can crush the crackers in a zip-lock bag with a rolling pin, whisk in the sugar, then stir in the melted butter.)

3. Using your fingers, press the mixture into the bottom of a 9-inch pie pan and up the sides. Be sure to press the bottom thoroughly so that the crumbs are evenly distributed. Set aside.

For the filling:

1. In a medium non-reactive saucepan, stir together the sugar, cornstarch, and salt until well combined.

2. Whisk in water and juice. Scrape the corners to incorporate all the dry ingredients.

3. Cook, stirring constantly, over medium heat for about 7 minutes, or until the mixture comes to a boil.

4. Boil, whisking constantly, for 1 minute, until mixture thickens and generously coats a spoon. Remove from the heat.

5. In a medium bowl, whisk the yolks well. Temper the yolks by whisking in about 1/2 cup of the hot lemon pudding.

6. Scrape the warm yolks into the hot pudding, whisking to blend in the yolk mixture before the eggs overcook.

7. Return the lemon pudding to the stove over the lowest heat and stir constantly for about 4 minutes.

8. Remove from the heat and add the butter, zest, and vanilla. Stir until the butter is completely melted.

9. Set the filling aside to cool for 30 minutes before spooning it into the graham cracker crust.

Make the meringue:

1. While the filling is cooling, Heat the oven to 350 degrees.

2. Beat the egg whites with the cream of tartar until they hold stiff peaks.

3. 3. Beat in the sugar, 1 tablespoon at a time. Continue to beat until very stiff but not dry.

4. Spoon the lemon filling into the graham cracker crust. Smooth with a small spatula or the back of a spoon.

5. Cover the filling with the meringue, creating peaks and swirls with the back of a spoon. Make sure that the meringue touches the edge of the pie shell all the way around.

6. Bake until the meringue is golden, about 12 to 15 minutes. Allow the pie to cool at room temperature for 1 hour, and then refrigerate until completely cold.