Lemon Curd Tart



To round out my family's Easter dinner this year I served two fruit tarts. The first was a baked raspberry & custard tart similar to one that I posted last July. The second was a lemon tart—the kind of classic Tarte au Citron that one finds in a French pastry shop. If you love lemon, this is probably one of your favorite desserts. I never get tired of this tart...served plain, with whipped cream or topped with meringue. Sprinkled with unadorned fresh berries or accompanied by a juicy berry compote, it is the quintessential early spring dessert.

In its simplest version, the tart is nothing more than a sweet cookie crust filled with lemon curd. It could not be easier to make. Many people think they can't make a tart because they think they can't make a good crust. And it is true that the classic flaky pastry (pâte brisée) that is used for pies and many tarts can require a bit of practice. But the sweet crust for this tart (and the raspberry tart) is quite easy. If you can mix up and roll a batch of sugar cookies, then you can make this crust.

The lemon curd too, is a snap to make. Stirred custards (which is what lemon curd is...a stirred custard of eggs and lemon juice, sweetened with sugar and enriched with butter) are typically considered to be difficult because if they are allowed to get too hot (over 180°F), the thick velvety custard will quickly turn into a mass of watery scrambled eggs. Most recipes for lemon curd direct you to cook the curd over very low heat or even in a double boiler in order to avoid this outcome. In my experience, these (time consuming) precautions aren't necessary. Lemon curd actually seems to be fairly resistant to curdling.

I have tried to locate an explanation of why this is the case, but have been unable to do so. I'm guessing there is something about the acidity of the lemon juice (most stirred custards are milk or cream based) and/or the large quantity of sugar necessary to sweeten the lemon juice that somehow affects the coagulation of the eggs. It is possible that these two things (alone or in conjunction) slow the coagulation process down or raise the temperature at which coagulation occurs. I am sure that if the curd were left on the heat and allowed to boil for any length of time...or to boil hard...that it would indeed scramble. But if when the curd has come just to the point of one or two boils breaking the surface, it is immediately poured out of the hot pan and into another container, it won't scramble.

The hot curd is finished with a process called "monter au buerre" or "mounting with butter". Basically, cold butter is whisked piece by piece into the lemon curd until it has been completely absorbed. Savory sauces are frequently finished this way because the emulsification of the butter into the sauce adds a nice sheen, a fluffier texture, and smoothness on the tongue. It also has the effect of softening strong and/or acidic flavors. And of course it does all of these things for the lemon curd, too. It also serves to cool the curd down fairly rapidly—which may have something to do with the fact that I have never had a curd scramble. If you are using a recipe that adds the butter at the beginning with the rest of the ingredients, follow the method and temperature directions given...or you may end up with scrambled eggs.

In posting this recipe, I realize that it comes too late for your Easter feast this year. But, there is always next year. Furthermore, there are still many events yet to come this Spring (Mothers' Day...a bridal shower...a graduation buffet...) for which a bright lemon tart, accompanied by some berries and softly whipped cream, would make the perfect dessert.

Lemon Curd Tart

(Tarte au Citron)

1 c. sugar
Zest of 3 lemons
2/3 c. strained lemon juice
4 eggs
4 oz. (1 stick) unsalted butter, cut into pieces (butter should be cold)
1 blind baked 9-inch tart shell (Pâte Sablé)

Combine the sugar, lemon zest and lemon juice in a medium saucepan and bring to a boil over high heat. In a medium-sized bowl, whisk the eggs until homogenous. When the lemon syrup boils, whisk it into the eggs in a thin stream.

Return this mixture to the saucepan and place over medium heat. Stir constantly until the mixture is visibly thickened—this will only take about 3 minutes. It's OK if one or two boils breaks the surface. 

Remove from the heat and whisk in the butter, piece by piece. When the butter is fully incorporated, strain the filling into the pre-baked crust. Place on a baking sheet and bake in a 350° oven until just set (it will still be a bit jiggly in the center)—15 to 20 minutes. Let the tart cool completely and chill. Serve with softly whipped cream or crème fraiche and fresh berries, if you like. Serves 8.

Notes:
• If you are not using the lemon curd immediately, strain the curd into a bowl and press a piece of plastic wrap to the surface. Chill. Makes about 2 1/2 cups.
• If you like the texture of lemon zest in your lemon curd, add the zest to the finished curd rather than at the beginning (since when added at the beginning it is strained out).

Sweet Tart Dough

(Pâte Sablé)

1/2 c. (1 stick) unsalted butter, at a cool room temperature
6 T. granulated sugar 
1 egg yolk
1 t. vanilla
1 1/4 c. all-purpose flour
1/3 cake flour

Briefly cream the butter and sugar together until smooth. Beat in the egg yolk and the vanilla. Add the flours and mix until just combined. Form the dough into a thick disk. Use immediately, or wrap in plastic and chill or freeze. Let the dough soften before rolling out.

On a lightly floured board (or between 2 sheets of plastic wrap), roll dough out to a thickness of 1/8- to 3/16-inch. Brush off the excess flour and transfer the dough to a greased tart pan. Ease the dough into the pan being careful not to stretch it and pressing it against the sides of the tart pan. Use your hands to gently cut the dough flush with the upper rim of the tart pan.

To blind bake, place the shell on a cookie sheet and bake in a 375° oven until set and golden—10 to 15 minutes. (It is not necessary to fill this crust with pie weights.)

Note: This amount of dough is enough for 1 ½ 9-inch tarts. I generally make up a double batch and divide it into 3 disks of dough. Freeze the disks that you don’t need. Use within 3 to 4 months.

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