The perfect lemon bar has a fierce filling and a strong supporting crust | Fort Worth Star-Telegram

When pastry chef Shuna Lydon was preparing for the opening of Bouchon, chef Thomas Keller’s supposedly casual and impossibly perfect French bistro in Napa Valley, he told her it would be the hardest thing she’d ever done — more difficult than her work creating desserts like white truffle egg creams at The French Laundry.

“He said, ‘You can do whatever crazy thing you want at French Laundry,’ ” she recalled. “'No one will know what it’s supposed to taste like. But everyone has an idea about what lemon tart is supposed to taste like.’”

Lemon bars are the home cook’s rendering of lemon tart, with a pressed-in crust and a simplified filling. But the desserts have the same appeal.

Both pay homage to the lemon in the same way a piece of sushi pays homage to the fish: The other elements are there only to set off one perfect ingredient. The sugar balances the lemon’s tartness, the butter smooths its acidic edges, and the flour mellows its intensity.

For people who are mad for lemon desserts, like me, no lemon bar is truly bad. But some are better than others: the ones with golden-brown crusts, the ones with just the right proportion of soft filling to crunchy base, the ones with creamy fillings that taste brightly of fresh lemon.

Like Beyonce and her backup dancers, the fierce, attention-grabbing filling should be supported by a crust that performs strongly on its own — and also does a brilliant job of making the star look good.

In many traditional recipes, the filling is a thick lemon curd, a slow-cooked spread of eggs, lemons and butter. In other recipes, the filling is more like a custard, simply blended, poured onto a hot crust and baked.

I’ve made lemon bars both ways, and hoped to prove my suspicion: that in this case, the easiest route is also the best. (Let’s call it kitchen wisdom, not confirmation bias.)

I set out to forge a single recipe that could stand out at a picnic or potluck, and also sweep confidently into a dinner party in tart form.

Lemon bars belong to the family of bar cookies: Along with brownies, pumpkin bars and dream bars, they are distinctly American sweets. Tarte au citron is one of the defining French desserts, and there are hardly any recipes more British than shortbread and lemon curd. Lemon chess pie, beloved in the South, has a similar flavor profile.

Tart like Lucy

But lemon bars have a thick bottom layer, between a pie crust and a cookie, that makes it possible to pick them up and eat them with fingers instead of a fork — a very American quality. The challenge for me, as for Lydon, is that everyone already seems to have a favorite recipe.

Lucy’s Lemon Squares have built a substantial fan base since 1969, when the recipe was first published in “The Peanuts Cook Book.” It is a basic and excellent recipe — and tart, like Lucy Van Pelt, the character for whom it’s named.

Baking blogs frequently rework the standard lemon bar with buzzy variations like cardamom crusts and Meyer lemon fillings (though Meyer lemons actually make dull lemon bars because they are so low in acidity).

And generations of bakers have been influenced by the changing versions in classic references like Junior League cookbooks and “Joy of Cooking,” which started out very plain but, over the decades, adopted new ingredients like double-acting baking powder and sweetened flaked coconut.

Those fluffy white shavings are pretty, and they are the basis for canonical American desserts like coconut cream pie and German chocolate cake. But they also usually contain preservatives like propylene glycol and sulfites. Since I have an embarrassing number of half-empty bags of dried unsweetened coconut in the pantry, I took a stab at making my own all-natural version. Just stirring the shreds together with sugar failed, but a quick simmer in sugar syrup was a howling success. (See “note” with recipe for a how-to.)

Coconut turned out to be the booster that lifts these lemon bars above the pack. A handful of sweetened coconut added to the crust gives it just the right fattiness to set off the sharp lemon, and helps keep the crust moist and crumbly.

It allowed me to reduce the sugar in the crust to a mere quarter of a cup. And it accomplishes all this without adding any noticeable flavor of coconut.

Every lemon bar filling is an attempt to transform lemon juice and sugar from liquid and grit into a unified, creamy fluff.

To do this, some cooks simmer the ingredients together, which changes their flavors; others add thickeners like egg yolk, flour and cornstarch that can make filling dense and stiff. Baking powder is an uncommon addition but a fantastically effective one.

Since baking powder is mostly baking soda (which reacts with the acidity of lemon) and cornstarch (which acts as a thickener), it is a multitasking ingredient here. Its leavening action puffs the filling, as it would puff a cake batter, adding air and softness.

The other thing to consider is a matter of personal taste: how thick you like the layers to be.

Like most pastry chefs, Lydon is precise about many things, including crust-to-filling ratios. Her preferred composition for a lemon bar, she said, is 1 to 1.7 — not quite the golden ratio, but unnervingly close.

And she has a very specific vision for what perfectly baked items like pie crust, shortbread and cookies ought to look like: GBD, or Golden Brown Deliciousness.

A browned crust, she said, shows that the flour and butter are cooked as they should be; a whitish crust, with undercooked ingredients, will have a raw taste and often a pasty texture.

“It’s the first thing you have to learn as a baker,” she said. “To know GBD when you see it.”