Lemons make me happy; they always have. I may run out of milk, eggs and coffee, but I am never without lemons. When I am feeling sad I'll open the refrigerator, reach for a lemon and run my fingers across the peel for the pure pleasure of the scent. It always improves my mood.
The lemon I don't like has never been grown, but the lemons from Sorrento are in a class by themselves. Something about the soil in that part of Italy makes lemons juicier and more fragrant than the ones we grow here. Their skin contains more aromatic oil as well. They are truly a joy to work with. They make fantastic lemonade, their candied peels are spectacular, and they're essential if you're making Limoncello. And in a tart... well, try it.
This one, with its perfect balance of sweet and tart, is wonderful made with ordinary lemons. Made with Sorrentos, however, it becomes truly extraordinary.
Begin by making the tart shell. If you have some nuts on hand – I like cashews in this crust but almonds or hazelnuts are also excellent – carefully toast a handful, then grind them up with 3/4 cup flour, 1/4 cup confectioners sugar and a pinch of salt. Cut half a stick of cold butter into the mixture with two knives, then stir in 3 tablespoons of olive oil and an egg yolk. Press the mixture gently into a 9 inch tart shell with a removable bottom. Chill if you have time; if not, bake in a 400 degree oven for about 15 minutes and allow to cool.
To make the filling, grate the zest from one lemon. Then squeeze 4 lemons and mix the juice with the zest, 3/4 cup sugar, 2 teaspoons cornstarch, 2 whole large eggs plus 2 large yolks. Whisk over medium heat until the mixture begins to boil; keep whisking for a couple more minutes. Remove from the heat, add ¾ of a stick of butter, cut into pieces, and whisk the mixture until the butter has vanished. Spread into the tart shell, allow to cool, then chill for at least 2 hours.