First, we’ll bake the dough a bit. I went for sugar dough, but you can use whatever. This recipe works well with your favourite cheesecake crust, and I won’t be judging you on that. But keep in mind the lemon filling doesn’t bake for too long, thus not staying in the oven enough for the dough to be done through. This means you have to plan for a solution that’s ok with being in the oven on its own. If you went with the same sugar dough as I did, just place it at the bottom of a rectangular baking tray you’ve lined with baking paper, punch it with a fork, and bake until it’s golden brown. Remove form the oven and let it cool down. Keep the oven running at 180°C, you’ll need it later.
Alright, let’s zest and juice those four lemons. If you went with key limes, I’m assuming they’re smaller than average, hence the difference with regular limes. You can mix the juice and zests, and set it aside.
Now, separate your egg yolks from the whites. Set the whites aside and, using a hand whisk, stir the yolks thoroughly. About two minutes in, pour in the condensed milk and stir again until it’s fully blended (that should take an additional two minutes of frantic arm movements if you’re going by hand). You can then pour the lemon juice and zest in, stirring like a madman until it seems to thicken a bit.
Pour that mixture oven the now cooled crust you’ve got in the baking tray. It’ll seem very liquid, which is fine. Bake for 25 minutes, then let it cool down completely, and set aside in the fridge. It’ll look slightly undercook, but it’ll continue to set once removed from the oven.
Now, I hate wasting egg whites, so let’s make some meringue. Beat them into firm peaks. Then, still whisking, slowly and delicately add in the caster sugar. When it’s done, pour the meringue on a baking tray in a shape that’s the same form and size as your now chilling cake. Try to make the meringue equally thick all the way so it cooks uniformly. Bake it at 125°C for 45 minutes.
Depending on the thickness of the meringue and your oven, your’ll get either a completely crisp one, or a crisp on the outside, tender on the inside result. It’ll be delicious regardless. Let it cool down, then place it on the now completed cake. Using a large knife, cut squares and serve immediately.
Best served with:
Really, anything that helps lessening the sugar burn is a plus, but remember this is still lemon. Sweet, yes, but quite bitter in its own right. I'd go with mint tea, that'd work well.