Lemon Nemesis

Steps

1. Preheat the oven to 325℉. Grease a 9 × 13-inch baking pan with a thin coating of neutral oil.

2. For the base, grind the crackers to a fine dust in a food processor, or put them in a heavy plastic bag and crush with a rolling pin. Combine the cracker crumbs, melted butter, and maple syrup in a medium bowl and mix quickly to moisten the crumbs. Scatter the crumbs across the bottom of the baking pan and gently press down, pushing them into the corners with the blade of your hand.

3. Bake the cracker base until you can smell it toasting and it has turned an even shade of almond brown, about 12 minutes. Remove from the oven.

4. Fill a large saucepot with a few inches of water for a double boiler and bring it to a simmer; make sure the bottom of the mixing bowl will hover above the water, not sit in it. Combine the eggs and yolks, lemon juice, sugar, and vodka in a large metal mixing bowl and whisk immediately to prevent the yolks from clumping with the sugar, then set the bowl over the simmering water. Cook, slowly stirring with a rubber spatula in a figure eight, until the mixture thickens into a custard that holds the trail of the whisk and measures 150℉ on an instant-read thermometer, about 10 minutes. Immediately remove from the heat and whisk in the cold butter, then cool the mixture over a bowl of ice water, stirring occasionally, until cool. Stir in the condensed milk and lemon extract.
5. Meanwhile, whip the cream in a large bowl to soft peaks. For the creamiest custard texture, the whipped cream should be floppy, not stiff.
6. Before you get to the final assembly, clear a flat, level space in your freezer to hold the baking pan so that the custard will freeze evenly.
7. Fold half of the whipped cream into the lemon mixture to lighten it, then add the rest, folding it
in until incorporated. Immediately pour the lemon filling into the cooled crust and spread it into the corners. Hustle the pan into the freezer to harden. After the top begins to freeze, press a sheet of plastic wrap or parchment paper against the surface of the filling to protect it from odors. (If planning to keep this in the freezer for any length of time, you may also want to double-wrap the pan in plastic wrap.) The lemon filling needs to freeze for at least 6 hours to be stiff enough to cut, but freezers vary. (The lemon nemesis can be prepared to this point up to 2 weeks in advance.)
8. Right before serving, make the meringue topping: Combine the egg whites, sugar, cream of tartar, vinegar, salt, and lemon extract, if using, in the bowl of a stand mixer or another large metal bowl and set over a pot of simmering water (the bottom of the bowl should not touch the water). Heat gently, whisking, until the egg white mixture feels uncomfortably hot to the touch, measuring about 150o F, about 5 minutes. Attach the mixer bowl to the stand, or use a hand mixer, and whip the egg whites on medium- high until the meringue looks glossy and thick and holds stiff peaks.
9. Spoon the meringue topping across the surface of the cake and smooth with an offset spatula or a pie server. If the cake has been frozen for days, transfer the cake to the refrigerator for about 15 minutes to gently thaw enough to slice.
10. Just before serving, brûleé the meringue with a blowtorch.
11. To serve, slice the cake into large squares. I generally divide it into 15 servings—rows of 5 divided by rows of 3—but you can serve any size you like. Lift out each piece with a pie server and transfer to serving plates. (If you have any difficulty prying the crust from the pan, pass the bottom of the pan over a hot stovetop burner to loosen the bottom crust.) If there happen to be leftovers, press a piece of plastic wrap against the cut surfaces and return to the freezer.