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Lemon bars occupy a quirky piece of culinary real estate, a sun-drenched lot on Lemon Lane, right between meringue pie and a fancy tarte au citron. It's a great part of town, where the rent is cheap and the neighbors friendly, quick to loan a cup of sugar to those in need.
Good thing, too, because lemon bars aren't snuggled down under a fluffy blanket of meringue, so they need a lot of sugar to balance their sour filling. That makes them sweeter than pie, and a little more custardy, though not to the extent of a yolky curd; unlike the French tarts next door, lemon bars aren't so rich.
Maybe that's why so many culinary architects err on the side of pragmatism, building lemon bars from whole eggs alone. It's a nice thought, but it's a softer foundation that's inclined to slowly ooze past the property line, so to speak, making for a messy snack. Some combat that problem with a thinner (some might say stingy) layer of filling, while others forge ahead and bake their bars as thoroughly as any cake, turning the custard all lumpy and weird. Then there are those who resort to a spoonful of cornstarch, accepting a murky custard as the price of stability.
But the lemon bars of my childhood were of a different sort, thick slabs as yellow as a daffodil and clear like a spring afternoon—no cloudy cornstarch in sight! I'm not sure what church lady I should credit for impressing me so, but that's the image that always comes to mind. With a great deal of trial and error, I've found that the trick to thick lemon bars without cornstarch is making the custard from equal parts whole eggs and yolks, by weight. That ratio offers enough extra yolks for structure, without turning the custard into an ultra-dense curd.
Of course, perfecting the filling would be for naught if my crust was but a pasty afterthought. And, while a good crust should be able to support the custard for days without devolving into a pile of mush, it should also serve as more than an edible plate. To that end, my version is barely sweetened, speckled with lemon zest, and buttery but light—like a classic sugar cookie crossed with lemon shortbread.
For a hybrid texture like that, I have to avoid the puff factor associated with creaming butter and sugar, while also steering clear of chewy eggs. (If you'll recall Cookie Science 101, eggless doughs are tenderer.) Those adjustments mean no friction or liquid ingredients to help dissolve granulated sugar, conditions that call for powdered sugar—once my greatest nemesis, but now a trusted friend.*
* More on that here, but tl;dr: Organic powdered sugar is generally made from raw cane sugar and tapioca starch, a combo that's more flavorful and less chalky.
By nature, the dough is better suited to a food processor, which can tear through cold butter to coat the flour in fat (thus shortening the potential length of each gluten strand). Since it all comes together lightning-fast, the butter stays cold, making for a dry meal that's more Dippin' Dots than dough, easily sprinkled and smooshed into a parchment-lined anodized-aluminum pan.
Yeah, that's a lot of adjectives to describe a baking pan, but they're all important. We'll get to the parchment later, but as for the rest? Well, non-aluminum options, like glass and ceramic, retain heat for ages, which can lead to overcooked lemon bars. Plus, their dimensions tend to make the bars too thin. Metal cake pans cool far more rapidly, but few folks own a set of stainless steel pans, and that's where anodized aluminum comes in.
It may not be a term you're actively aware of, but anodization is what makes iPad minis look so boss, and why certain lightweight cake pans never rust. Anodization is a manufacturing process that sends an electrical charge through a sheet of metal while it soaks in an acidic bath of electrolytes. The result of this, shall we say, shock therapy is a metal so chill, it won't even react when confronted by acidic liquids looking for a fight. Without anodization, citric acid + unfinished aluminum = janky, old-tin-can-flavored bars. Mmmm, boy!
With the crust in the right pan and baking to a golden brown, I prepare the filling on the stove. Again, it's vitally important that everything from the pot to the whisk be nonreactive (in those cases, that typically means stainless steel), but it's otherwise dead easy to prepare. Just combine the eggs and yolks, add the lemon zest and sugar, then whisk until smooth.
Yeah, that's right, straight in the pan—no tempering required! Ladling hot liquids while whisking with one hand is like having to rub your head and pat your tummy—annoying at best. Doubly so, considering the extra dishes. Tempering is reasonable when dealing with eggs and hot liquids, which are inherent to any infusion (like vanilla steeped in milk). But, when combining eggs with room-temperature ingredients, like fresh lemon juice, there really isn't any need so long as everything is warmed up slowly over low heat.
Once you've knocked off the chill, you can turn up the dial and let a digital thermometer be your guide. While egg yolks and whites normally coagulate at around 140° and 150°F, respectively, sugar delays that process by about 10 degrees. To get a custard that's thick enough to slice, it needs to go a little higher still, to about 170°F.
Cooking on the stovetop allows for precise control over the custard's final texture, which is vastly preferable to jiggling a hot pan in the oven and wondering exactly how wobbly "wobbly" should be (or else trying to test the relatively shallow filling layer with a Thermapen and hoping you don't hit the crust).
Stovetop cooking also means I can strain the custard as it goes over the crust, eliminating coagulated lumps of chalazae and bits of zest that have already given up their lemony aroma. After that, I cover my lemon bars with foil to trap steam, then toss them in the oven, where a few minutes of warmth will spread the filling to a perfectly level, mirror-smooth finish.
Necessary? No. But it's a simple touch that makes lemon bars as stunning as any French tart.
Once cooled to room temperature, the lemon bars are chilled and transferred to a cutting board (hence the aforementioned parchment to pull them loose). You might be tempted to file that under "fussy, cheffy steps I don't care about," but wait! Cutting the bars in the pan will a) dull your knife and b) scratch your pan, c) making future cakes or crusts more likely to stick and d) ruining the anodized surface, which e) negates its nonreactive properties, meaning, oh, f) your future lemon bars will taste like a dirty penny.
Besides, with a cutting board, you'll be able to slice 'n' dice the bars into the most gorgeously geometric squares. Pack them up for picnics and potlucks (the high-sugar, high-acid bars will do fine at room temperature), or serve them straight from the fridge, cold and refreshing like lemonade.
Like any self-respecting American, I finish my lemon bars with a dusting of powdered sugar. It may not add much beyond a hint of sweet against the sour filling, but it's hard to overstate the visual appeal—a field of flawless white to make edges look more crisp and the custard more radiant.
If powdered sugar isn't usually your cup of tea, you may appreciate the mellower sweetness of organic brands; just be aware that the organic sugar will begin to melt within 15 minutes. Conventional brands taste a little chalkier, but they'll widen that window to about a half hour.
Whatever you choose, don't forget to save your used-up lemon rinds! Even when zested, juiced, cut, and otherwise abused, they're the basis of my no-cook Fresh Lemon Syrup. It's great to have for whipping up everything from cocktails to vinaigrette, but it's also the key to a few citrusy garnishes that'll make the neighbors jealous: Lemon Chantilly and crispy candied pistachios.
Together, they make a community of citrus anyone would want to live in...or eat.