Setting the Standard

• The filling for traditional lemon pie follows a standard technique that's used for other custard-type fillings, such as pastry cream. To make it, you whisk cornstarch and sugar together and then dissolve them in cold water. Heat the mixture gently over a double boiler, stirring regularly, until it begins to thicken. While it's warming, whisk egg yolks in a separate bowl. You'll stir part of the hot sugar mixture gently into the egg yolks, to warm and dilute them, then combine the yolks into the main mixture and simmer it a few minutes longer. Finally, the filling is enriched and flavored with lemon juice, lemon zest, butter and sometimes food coloring to give it a stronger yellow tint.

Room for Improvement

• Once you've gotten the hang of this basic technique, you'll be able to make a good lemon pie more often than not. Still, there are a number of ways things can go wrong. The cornstarch mixture might thicken unevenly, or it might leave lumps in the filling. The egg yolks can become overcooked if you combine them with the hot mixture too quickly or don't stir regularly, leaving grainy flecks of cooked egg in your finished filling. These can be strained out, but the end result is somewhat impaired. Chef Thomas Keller, of The French Laundry and Bouchon, popularized an alternative technique inspired by a dessert called sabayon.

Sabayon and Zabaglione

• Sabayon is a French dessert, inspired in turn by a very similar Italian custard called zabaglione. Zabaglione uses a dessert wine called Marsala as its base, while sabayon relies on light, crisp champagne. Sabayon is made by whisking egg yolks and sugar over a double boiler until they're frothy, then adding the champagne and whipping the mixture to a light froth. The egg yolks thicken the basic mixture, as they do in other custards, but it's also thickened -- as with meringue, or whipped cream -- by the frothing process.

Sabayon Lemon Tart

• In Keller's version of the dessert, the process is identical, but it's lemon juice rather than champagne or Marsala that's whisked into the egg yolks. The lemon juice is the only liquid used in the filling, as opposed to forming a relatively small part of the whole as it would in a conventional lemon pie. Ordinarily that might make the tart mouth-puckeringly unpleasant, but the whisked-in air mutes the lemon's intensity, leaving it pleasantly brisk and refreshing. The tart isn't finished with meringue, but instead is caramelized under a broiler for just a few seconds.