The Cook's Illustrated Cookbook (336 page)

WHY THIS RECIPE WORKS

Some of us have been served Key lime pie in restaurants and found it disappointing, usually harsh and artificial tasting. We wanted a recipe for classic Key lime pie with a fresh flavor and silky filling. Traditional Key lime pie is usually not baked; instead, the combination of egg yolks, lime juice, and sweetened condensed milk firms up when chilled because the juice’s acidity causes the proteins in the eggs and milk to bind. We found that just one simple swap—from bottled, reconstituted lime juice to juice and zest from fresh limes—gave us a pie that was pungent and refreshing, cool and yet creamy, and very satisfying. We also discovered that while the pie filling will set without baking (most recipes call only for mixing and then chilling), it set much more nicely after being baked for only 15 minutes. We tried other, more dramatic, departures from the “classic” recipe—folding in egg whites, substituting heavy cream for condensed milk—but they didn’t work. Just two seemingly minor adjustments to the classic recipe made all the difference in the world.

SERVES 8

Despite this pie’s name, we found that most tasters could not tell the difference between pies made with regular supermarket limes (called Persian limes) and true Key limes. Since Persian limes are easier to find and juice, we recommend them. The timing here is different from other pies; you need to make the filling first, then prepare the crust.

PIE

TOPPING (OPTIONAL)

1. FOR THE PIE:
Whisk egg yolks and lime zest together in medium bowl until mixture has light green tint, about 2 minutes. Whisk in condensed milk until smooth, then whisk in lime juice. Cover mixture and set aside at room temperature until thickened, about 30 minutes.

2.
Meanwhile, prepare and bake crust. Transfer pie plate to wire rack and leave oven at 325 degrees. (Crust must still be warm when filling is added.)

3.
Pour thickened filling into warm prebaked pie crust. Bake pie until center is firm but jiggles slightly when shaken, 15 to 20 minutes. Let pie cool slightly on wire rack, about 1 hour, then cover loosely with plastic wrap and refrigerate until filling is chilled and set, about 3 hours.

4. FOR THE TOPPING, IF USING:
Once pie is chilled, use stand mixer fitted with whisk to whip cream and sugar on medium-low speed until foamy, about 1 minute. Increase speed to high and whip until soft peaks form, 1 to 3 minutes. Spread whipped cream attractively over top of pie.

WHY THIS RECIPE WORKS

Most everybody loves lemon meringue pie—at least the bottom half of it. The most controversial part is the meringue. On any given day it can shrink, bead, puddle, deflate, burn, sweat, break down, or turn rubbery. We wanted a pie with a crisp, flaky crust and a rich filling that would balance the airy meringue, without blocking the clear lemon flavor. The filling should be soft but not runny, and firm enough to cut but not gelatinous. Most important, we wanted a meringue that didn’t break down and puddle on the bottom or “tear” on top. We consulted our food scientist, who told us that the puddling underneath the meringue is from undercooking. The beading on top of the pie is from overcooking. We discovered that if the filling is piping hot when the meringue is applied, the underside of the meringue will not undercook; if the oven temperature is relatively low, the top of the meringue won’t overcook. Baking the pie in a relatively cool (325-degree) oven also produces the best-looking, most evenly baked meringue. To further stabilize the meringue and keep it from weeping (even on hot, humid days), we beat in a small amount of cornstarch.

See “APPLYING A MERINGUE TOPPING” illustrations that follow recipe.

SERVES 8

You can use
ALL-BUTTER
or
CLASSIC SINGLE-CRUST PIE DOUGH FOR CUSTARD PIES
for this pie. Make the pie crust, let it cool, and then begin work on the filling. As soon as the filling is made, cover it with plastic wrap to keep it hot and then start working on the meringue topping. You want to add hot filling to the cooled pie crust, apply the meringue topping, and then quickly get the pie into the oven.

FILLING

MERINGUE

1. FOR THE FILLING:
Adjust oven rack to middle position and heat oven to 325 degrees. Bring water, sugar, cornstarch, and salt to simmer in large saucepan, whisking constantly. When mixture starts to turn translucent, whisk in egg yolks, two at a time. Whisk in lemon zest and juice and butter. Return mixture to brief simmer, then remove from heat. Lay sheet of plastic wrap directly on surface of filling to keep warm and prevent skin from forming.

2. FOR THE MERINGUE:
Bring water and cornstarch to simmer in small saucepan and cook, whisking occasionally, until thickened and translucent, 1 to 2 minutes. Remove from heat and let cool slightly.

3.
Using stand mixer fitted with whisk, whip egg whites, vanilla, and cream of tartar on medium-low speed until foamy, about 1 minute. Increase speed to medium-high and whip whites to soft, billowy mounds, about 1 minute. Gradually add sugar and whip until glossy, stiff peaks form, 2 to 3 minutes.

4.
Meanwhile, remove plastic from filling and return to very low heat during last minute or so of beating meringue (to ensure filling is hot).

5.
Pour warm filling into cooled prebaked pie crust. Using rubber spatula, immediately distribute meringue evenly around edge and then center of pie, attaching meringue to pie crust to prevent shrinking. Using back of spoon, create attractive swirls and peaks in meringue. Bake until meringue is light golden brown, about 20 minutes. Let pie cool on wire rack until filling has set, about 2 hours. Serve.

WHY THIS RECIPE WORKS

When this French dessert—basically an apple tart in which the apples are caramelized and the tart is served upside down—first came to this country, all sorts of different recipes for it appeared. Some were based on traditional French formulas, but others were highly Americanized. When we tried the latter, we were disappointed—we got desserts that tasted like apples coated with caramel sauce or, worse, were just an unidentifiable caramel glop. We wanted a tart that tasted like caramelized apples and looked great, too. The first step of our tarte Tatin took place on the stovetop, not in the oven. We arranged apple quarters in concentric circles in a skillet on their cut side so we could fit more fruit, and flipped the apples over as they caramelized. We prepared the caramel right in the skillet with the apples so the flavors could meld, then covered the syrup-soaked apples with an egg pastry that contained confectioners’ sugar rather than granulated sugar, which can make the dough grainy. After baking our tarte Tatin, we flipped the tart over, revealing concentric circles of apples glazed with golden caramel. And for French finish, we mimicked the tart whipped cream, crème fraîche, by whipping heavy cream with sour cream.

See “ASSEMBLING TARTE TATIN” illustrations that follow recipe.