Lemon Curd Tartlets

Over the weekend, I made lemon curd tartlets for our friend Tomomi's birthday. In an effort to make lemon bars look a little more elegant, I baked them in mini cupcake liners. Not knowing that shortbread puffs up while baking, it left little room for the lemon curd. Hence, 'tartlets' that resemble thumbprint cookies. Anyhow, everyone seemed to enjoy them. The shortbread was light and buttery; the lemon curd—tart and sweet, not to mention super lemony.

The Ultimate Lemon Butter Bar recipe hails from Rose Levy Beranbaum's book, Rose's Christmas Cookies via Epicurious. She gives extensive instructions on how to make the shortbread, including how to make it with a food processor. I chose to make it by hand as recommended. If you wish to see the other method as well as how to make bars, you may find those instructions on the Epicurious link. I have edited the recipe to explain how to make my version. See those edits after the jump.

The Ultimate Lemon Butter Bar

Epicurious | November 1998

by Rose Levy Beranbaum

Rose's Christmas Cookies

Yield: Makes 1 1/2 dozen 2 2/3-inch by 1 1/3-inch bars

Shortbread Base

10 tablespoons unsalted butter (cold) (5 ounces = 142 grams)

2 tablespoons powdered sugar (0.5 ounce = 14 grams)

2 tablespoons granulated sugar (0.75 ounce = 25 grams)

1 1/4 cups bleached all-purpose flour (dip and sweep method) (6.25 ounces = 180 grams)

Lemon Curd Topping

4 large egg yolks (2 full fluid ounces = 2.5 ounces = 74 grams)

3/4 cup sugar (5.25 ounces = 150 grams)

3 fluid ounces (use a liquid measuring cup) lemon juice, freshly squeezed (about 2 1/2 large lemons) (3.25 ounces = 94 grams)

4 tablespoons unsalted butter (softened) (2 ounces = 57 grams)

Pinch of salt

2 teaspoons lemon zest (finely grated) (4 grams)

2 tablespoons powdered sugar for dusting (0.5 ounce = 14 grams)

SHORTBREAD BASE

Electric Mixer Method or by Hand

In Scotland, it is said that the best shortbread is mixed with the fingers and that each woman's fingers lend something distinctive and special to the finished cookie. I find that the texture is more delicate when the dough is mixed with the fingers rather than in a machine. For either method, use superfine sugar for the best texture and be sure to soften the butter.

1) In a medium bowl, whisk together the sugars.

2) In a large bowl, cream the butter with the sugars until light and fluffy.

3) With your fingers or with the electric mixer, mix in the flour until incorporated.

4) If using the mixer, add the flour in 2 parts.

5) Place 1 oven rack in the middle of the oven.

6) Preheat oven to 325°F.

7) Line muffin tins or tart tins with mini cupcake liners.

8) Pat the dough into the prepared pan. Take a small piece of the dough, about 1 tablespoon, and roll it into a ball. 

9) Place the ball of dough and press into the center, allowing it to up the sides of the muffin tin or tart tin. This will create an indentation where you will fill the lemon curd. Repeat until you use up all of the dough.

10) Use a fork to prick the dough all over on the bottom.

11) Bake for about 20 to 30 to 40 minutes or until the edges are lightly browned and the top is pale golden (do not brown).

12) Prick the dough again with a fork if it rises in the oven.

13) While the shortbread is baking, prepare the Lemon Curd Topping.

LEMON CURD TOPPING

14) Have a strainer, suspended over a bowl, ready near the range.

15) In a heavy noncorrodible saucepan, beat the egg yolks and sugar with a wooden spoon until well blended.

16) Stir in the lemon juice, butter, and salt.

17) Cook over medium-low heat, stirring constantly, for about 6 minutes, until thickened and resembling hollandaise sauce, which thickly coats a wooden spoon but is still liquid enough to pour. (A candy thermometer will read 196°F.)

18) The mixture will change from translucent to opaque and begin to take on a yellow color on the back of a wooden spoon. It must not be allowed to boil or it will curdle. (It will steam above 140°F. Whenever steaming occurs, remove the pan briefly from the heat, stirring constantly to prevent boiling.)

19) When the curd has thickened, pour it at once into the strainer.

20) Press it with the back of a spoon until only the coarse residue remains.

21) Discard the residue.

22) Stir in the lemon zest.

23) When the shortbread is baked, remove it from the oven, lower the temperature to 300°F., pour the lemon curd on top of the shortbread into each tart shell, and return it to the oven for 10 minutes.

24) Cool the lemon curd–topped shortbread completely in the pan on a wire rack.

25) Refrigerate the pan for 30 minutes to set the lemon curd completely before cutting into bars.

Store: In an airtight container at room temperature, or in the refrigerator or freezer.

Keeps: 3 days at room temperature, 3 weeks refrigerated (individually wrapped in plastic wrap to prevent drying), or 3 months frozen.

Smart Cookie

• Cooking the topping before pouring it into the shortbread ensures crispness as opposed to the usual pastiness of the pastry.

• Returning the curd to the oven, where it will be exposed to heat without stirring, causes the yolk to rebond, making it firm enough to cut after cooling.

• If each lemon is heated about 10 seconds in a microwave oven on high power and rolled around while pressing on it lightly, it will release a significantly greater quantity of juice.

• An aluminum pan should not be used to prepare the lemon curd because it will react with the egg yolks, turning them chartreuse.

• Sugar raises the coagulation point of the egg yolk. It also protects it from premature coagulation during the addition of the lemon juice. If the juice were added directly to the unprotected yolk, the yolk would partially coagulate and, when strained, a large percentage of it would be left behind in the strainer. Be sure to mix the sugar well with the egg yolks before adding the juice.