Crust
14 whole graham crackers
1/4 cup sugar
1/4 teaspoon salt
6 tablespoons unsalted butter, melted and still warm
Filling
2 14-ounce cans condensed milk
1 1/4 cups strained lemon juice (from the 2 zested lemons below plus an additional 4–6 lemons)
Zest of 2 lemons
8 large egg yolks
Chantilly cream
2 cups heavy cream
1/2 teaspoon vanilla extract
1/4 cup confectioners’ sugar
To make the crust
Heat the oven to 325°F. Break the graham crackers into small pieces and place in the bowl of a food processor along with the sugar and salt. Pulse 8 times, until the cracker crumbs are semi-fine (they shouldn’t be powdery but not in large shards either) and the crackers and sugar are combined. Pour in the butter and pulse until the butter is blended in and the mixture isn’t crumbly and holds its shape when you squeeze it, about twelve 1-second pulses. Transfer the crust to a 9-inch springform pan and push and press the crumb mixture into the bottom and two-thirds of the way up the sides of the pan. Use the bottom of a measuring cup to press the crust into place. Set aside.
To make the filling
Whisk the condensed milk with the lemon juice and set aside. Whisk the zest with the egg yolks in a medium bowl until pale, 30 to 60 seconds, and then whisk in the lemon juice-condensed milk mixture.
Place the springform pan on a rimmed baking sheet, pour the mixture into the crust, and carefully transfer the baking sheet to the oven. Bake until the center jiggles slightly, like a soft-setting custard, about 25 minutes. Remove from the oven and cool for 1 hour on a cooling rack. Loosely cover the pan with plastic wrap (be careful not to let the plastic wrap touch the top of the pie) and freeze for at least 6 hours or overnight.
To make the chantilly cream
Pour the heavy cream into the bowl of a stand mixer (or in a large bowl if using a hand mixer). Add the vanilla and sift in the confectioners’ sugar. Whip on low speed to combine and then increase the speed to medium-high and whip until medium-stiff peaks form, about 1 1/2 minutes.
Before serving, wrap a wet, warm kitchen towel around the edges of the springform pan to release the pie from the pan’s sides. Unclasp the pan and remove the pie. Fill a pitcher with hot water, dunk your knife in, wipe off the blade, and slice. Top with a dollop of chantilly cream and serve immediately, or keep in the freezer for up to 1 week.