This is an old favorite that I make several times a year. It’s best made with Meyer lemons. The tart filling is my idea of the ultimate curd, buttery and lemony in perfect balance. The combination of creamy, tart curd and crisp shell makes it an ideal ending for a rich winter dinner. Make the curd while the tart shell chills and bakes.
8 SERVINGS
Tart Shell
1¼ |
cups all-purpose flour, plus more for rolling |
1 |
tablespoon sugar |
|
Pinch salt |
8 |
tablespoons (1 stick) unsalted butter, cut into small pieces |
2–3 |
tablespoons ice water |
Curd
2 |
large eggs |
2 |
large egg yolks |
½ |
cup sugar |
¼ |
teaspoon salt |
|
Zest of 1 lemon |
½ |
cup lemon juice |
6 |
tablespoons (¾ stick) cold unsalted butter, cut into pieces |
For the tart shell: Butter a 9-inch tart pan with a removable bottom. Set aside.
Combine the flour, sugar, salt and butter in a food processor or large bowl and cut them together until the mixture resembles coarse cornmeal. Add the water 1 tablespoon at a time, stirring constantly or processing until the mixture just begins to come together.
Remove the dough from the bowl and knead lightly and briefly to make a smooth mass. Wrap it in plastic wrap and refrigerate for at least 30 minutes.
On a well-floured work surface, roll the dough into a circle about 11 inches in diameter. Roll the dough back onto the rolling pin and transfer it to the tart pan. Unroll the dough and gently press it into the pan. Trim the excess dough to 1 inch from the pan edge and tuck the extra dough between the pan and the dough rim to make a sturdier, taller edge. Refrigerate for 30 minutes.
Heat the oven to 425 degrees. Prick the crust with a fork. Line the crust with a sheet of aluminum foil and fill it with rice, dried beans or pie weights. Bake for 10 minutes. Remove the foil and beans and bake until the crust is golden brown and firm, about another 15 minutes. Remove from the oven and let cool to room temperature.
For the curd: Beat the eggs, yolks, sugar and salt in a small saucepan until smooth and light colored.
Add the lemon zest, lemon juice and butter and cook over medium heat, stirring constantly, until the butter melts, about 2 minutes.
Reduce the heat to medium-low and continue cooking and stirring for about 5 minutes, or until the curd is thick enough to coat the back of a spoon and your finger leaves a definite track when you draw it across the spoon. The curd should resemble a thick hollandaise. Pour it through a fine-mesh strainer into a chilled bowl.
Spoon the curd into the prepared crust and smooth the top with the back of a spoon. Refrigerate for at least 1 hour to set the lemon curd. Serve cold.
Lemon curd is a paradox in a saucepan: it’s rich and creamy; it’s tart and fresh. Those are the characteristics that make it delicious; they’re also the characteristics that make it seem impossible to prepare. Think about it: What happens when you pour lemon juice into milk? How would you make that taste good? The answer lies in a particularly basic and very useful bit of food chemistry.
Citrus curds are creamy despite having little or no cream in them. Instead, the luscious texture is supplied by cooked beaten eggs. But citrus curds also are smooth, not like scrambled eggs at all. How does this work?
First, you need to understand a little egg chemistry. Eggs are full of strands of protein that at room temperature are tightly curled and separate. As they heat up, the protein strands relax and unfold. As they unfold, they bump into other protein strands and link up, capturing the liquid that is present in the egg. This is called coagulation. Typically, with pure egg, the white begins to set between 145 and 150 degrees and is firm at 160 degrees. By 180 degrees the protein strands have tightened to the point that all the liquid is wrung out. (Egg proteins are not alone in this behavior; that’s what happens when you overcook a chicken breast, too.)
That 145-to-160-degree window is pretty hard to hit, especially over a live flame, which is precisely why perfectly scrambled eggs are such a miracle. Add sugar, however, and an interesting thing happens. The window opens wider. The sugar isolates the protein strands, moving them farther from each other and keeping them apart longer. This raises the temperature at which they coagulate. Cooks have been taking advantage of this chemical reaction for centuries. The phenomenon is the secret behind both cooked custards and zabaglione, the Italian dessert consisting of egg yolks, sugar and, traditionally, Marsala that is beaten and cooked until it is a slightly foamy cream.
In fact, if you take zabaglione, replace the liqueur with lemon juice and add butter, you have lemon curd.
But there are lemon curds and there are lemon curds. To come up with the version I liked best, I first analyzed a dozen recipes from different cookbooks. Although the techniques were basically the same, the proportions of ingredients varied greatly. Some recipes, for instance, called for whole eggs, some for yolks and some for a combination of the two. I made curds with pure yolks and with an equal volume of whole eggs and compared them. Both methods worked equally well, but there were major differences in the outcomes. Made with yolks, the curd was stiffer and the flavor richer and more custardy. Made with whole eggs, the curd was lighter-colored, the set was softer, and the flavor was more intensely fruity. I ended up compromising, using 2 whole eggs and 2 egg yolks to give the curd a slightly smoother flavor and slightly firmer set.
The amount of sugar in the recipes varied even more, ranging from ¼ cup to 1 cup. A recipe I made with ½ cup of sugar was well balanced. I tried ¾ cup and found that it was too simply sweet, particularly in the aftertaste. I never added as much as 1 cup of sugar.
Butter amounts varied from 2 tablespoons to 8 tablespoons. I found that the amount of butter resulted in much more subtle differences than the amount of sugar. Curd made with only a little butter was more tart and fruity. The more butter I added, the more complex the flavors became, but also the more the fruit flavor was masked. I preferred about 6 tablespoons of butter. I can certainly see the argument in favor of less, though, particularly if you want a cleaner, fresher flavor.
I also made curds with different citrus fruits. Although lemon was the exemplar (and Meyer lemon even better), lime was very nice, with a pointed acidity and a slightly grassy, herbal quality. Orange was softly acidic and delicately floral. I tried blood oranges, too, but that was the only washout. When blood oranges are cooked, the vivid red color fades to a bruised purple, and the intriguing berry quality becomes nasty and artificial-tasting.
Most interestingly (at least to a food wonk), I tried to make curd with plain water to test the effect of liquid with no acidity and wound up with sweet, watery scrambled eggs. Acidity lowers the coagulation temperature and obviously plays a very important role in tempering the action of the sugar.
The most amazing thing about curd isn’t its many variations but the one thing all versions have in common: curd is dead simple to make. In fact, as delicate as it may seem, you don’t even need to use a double boiler; you can make it in a single small saucepan. Just use a common pastry chef’s trick: bring the mixture quickly to a boil over high heat, then strain out any bits of curdled egg. I recommend a path somewhere between the cautious double boiler and the bold chef’s methods—cooking the curd over medium heat while using cold butter to moderate its temperature, then reducing the heat once the butter melts and continuing to cook until the curd thickens.
When the curd is done, it should coat the back of a spoon like a moderately thick hollandaise. It should be thick enough that when you draw your finger across the spoon, you divide the coating into two distinct sections. It will set more as it cools. Curious about the temperature, I measured it a couple of times and found that the mixture began to smooth out and thicken slightly at about 165 degrees and was finished at about 185 degrees.
The key to success is making sure the eggs and sugar are well beaten before you add the remaining ingredients. That’s the only way to temper the proteins sufficiently. When I tried making curd by simply mixing everything together, I got fine bits of curdled whites, even after straining.