Ask the Test Kitchen: Love lemon curd? Make your own

Q: How long can you keep commercial lemon curd once it’s opened? What are some other uses for lemon curd?

— A reader from Plymouth, Minn.

A: Lemon curd is a thick, bright yellow spread similar to jelly in texture. It has a tart lemon taste balanced with some sweetness.

Once opened, a jar of lemon curd should be refrigerated and used within six months for best quality, according to the folks at the J.M. Smucker Co., maker of the Dickinson’s brand of lemon curd. Unopened, the jar should have a best-if-used-by date on the label that you should follow. If you make your own lemon curd from scratch, use it within one week.

If you’re not familiar with lemon curd, it’s a mixture of lemon juice, sugar, butter, whole eggs and egg yolks. The mixture is cooked together until it thickens and the eggs are tempered and heated to a safe temperature without them totally cooking. Once thickened, the mixture is cooled and most of the time strained. You can make the curd with most any citrus. Using lime or orange juice is common.

Lemon curd is great spread on toast, biscuits or muffins. You can use the curd as a filling for pre-baked tarts or in crepes. Spread lemon curd in between cake layers or spoon dollops of it on pancakes or ice cream. Mix a few spoonfuls of lemon curd into whipped topping and use as a frosting for a cake.

While most grocery stores carry lemon curd, making your own is easy. This way, you can adjust the lemon flavor to taste. But keep in mind that lemon curd should pack a good lemony punch.

You’ll need a little patience and a watchful eye when cooking the mixture, taking care that the eggs don’t cook too much and the sugar doesn’t brown.

Don’t be put off by taking the time to zest and squeeze the juice from lemons. Always remember: Zest the lemons (or other citrus) first before you squeeze out the juice. (If you don’t use all the zest, put it in a plastic bag and freeze it.)

Here’s a basic lemon curd recipe:

In the top of a double boiler over simmering water, whisk together 2 whole eggs and 2 egg yolks. Whisk in 1/2 cup sugar and 1/3 cup fresh lemon or lime juice. Continue whisking until the mixture thickens, about 5 minutes. Do not let the mixture boil or it will curdle. Remove the pan from over the simmering water and whisk in 6 tablespoons butter, in pieces, until melted. Cool to room temperature, about 30 minutes. Place the curd in the refrigerator and chill; it will continue to thicken. Use as desired. This makes about 2 cups. Keep it refrigerated.

Here are two recipes that make terrific use of lemon curd.

Lemon Bars with Olive Oil and Sea Salt

Makes: 24 bars

Preparation time: 25 minutes

Total time: 1 hour (plus cooling time)

For the crust:

1 1/4 cups all-purpose flour

1/4 cup granulated sugar

3 Tbsp. confectioners’ sugar, plus more for sprinkling

1 tsp. finely grated lemon zest

1/4 tsp. fine sea salt

10 tablespoons well-chilled unsalted butter, cut into cubes

For the curd:

4 to 6 large lemons

1 1/2 cups sugar

2 large eggs plus 3 yolks

1 1/2 tsp. cornstarch

Pinch of sea salt

4 Tbsp. unsalted butter, cut into pieces

1/4 cup fruity olive oil

Flaky sea salt, for sprinkling

Preheat the oven to 325 degrees and line a 9-by-9-inch baking pan with enough parchment to hang over a good inch or 2 from the sides. These will be the handles to help lift the bars out of the pan.

To make the shortbread base, pulse together the flour, granulated sugar, confectioners’ sugar, lemon zest and salt in a food processor, or whisk together in a large bowl. Add butter and pulse (or use two knives or your fingers) to cut the butter into the flour until a crumbly dough forms. Press dough into prepared pan and bake until shortbread is pale golden all over, 30 to 35 minutes.

While the shortbread is baking, prepare the lemon curd: Grate a generous 1 1/2 teaspoons of zest from lemons and set aside. Squeeze lemons to yield 3/4 cup juice.

In a small saucepan, whisk together lemon juice, sugar, eggs and yolks, cornstarch and fine sea salt over medium heat until boiling and thickened, 3 to 5 minutes. Make sure mixture comes to a boil or the cornstarch won’t activate. But once it boils do not cook for longer than 1 minute or you risk the curd thinning out again. Remove from heat and strain into a bowl. Whisk in butter, olive oil and lemon zest.

When the shortbread is ready, take it out of the oven and carefully pour the lemon curd onto the shortbread base; return the pan to the oven. Bake until topping is just set, about 10 to 15 minutes more. Allow to cool to room temperature, then refrigerate until cold before cutting into bars. Sprinkle with confectioners’ sugar and flaky sea salt right before serving.

Adapted from and tested by Susan Selasky for the Free Press Test Kitchen. Analysis per 1 bar.

183 calories (49 percent from fat), 10 g fat (4 g saturated fat), 22 g carbohydrates, 2 g protein, 107 mg sodium, 56 mg cholesterol, 0 g fiber.

Mixed Berry Tart with Lemon Curd Filling

Serves: 8 (4-inch tarts)

Preparation time: 15 minutes

Total time: 1 hour, 30 minutes

The pastry dough is easy to work with in this recipe. If you don’t have individual tart pans, you can use a 10-inch tart pan and make one tart. These tarts get a deep lemony flavor from the lemon curd. Serve the tarts individually or cut them in half to serve more.

For the dough:

2 to 2 1/4 cups all-purpose flour

14 Tbsp. unsalted butter, well-chilled, cut into small pieces

1 large egg, lightly beaten

2 Tbsp. sugar

1 Tbsp. chilled heavy cream or half-and-half

2 tsp. fresh lemon juice

1 tsp. salt

For the lemon filling:

1/2 cup heavy cream

1 cup Lemon Curd (see Lemon Bars recipe)

4 cups mixed berries such as fresh raspberries, blueberries and blackberries

Have ready eight 4 3/4-inch fluted tart pans with removable bottoms.

In a food processor fitted with the metal blade, place all the dough ingredients and pulse until the dough starts gathering together in big clumps. If the dough is too soft, add more flour a tablespoon at a time. Turn the dough out onto a counter and gather it together.

Shape the dough into an 8-inch log and divide it into eight equal pieces. On a lightly floured surface, roll a piece of dough into a 5-inch round. Gently press the dough into a tart pan. Repeat with the remaining dough. Put the tarts on a baking sheet and chill in the refrigerator for 15 minutes.

Meanwhile, heat the oven to 400 degrees.

Cut out eight roughly 6-inch-square pieces of foil and spray one side lightly with nonstick cooking spray. Line each tart with a square of foil, oiled side down, making sure the top edge of the tart is covered. Place a handful of pie weights, raw rice or dried beans into each lined tart. Transfer the tarts (still on the baking sheet) to the oven and bake until the crust turns golden brown and starts to pull away from the sides of the pans, 25 to 30 minutes.

Remove from oven and cool the tarts on the baking sheet on a rack for 5 minutes. Carefully remove the lining and weights. Let cool completely on the baking sheet on the rack.

In a medium bowl, whip the cream to soft peaks. Add the lemon curd and gently fold together with a rubber spatula until combined. Divide the mixture among the pastry shells and smooth the filling with a spatula or the back of a spoon. Carefully remove the outer rings and bottoms of the tart pans and arrange the tarts on a large platter. Top each tart with a mixture of raspberries, blueberries and blackberries, and serve immediately.

Cook’s note: You can combine the lemon curd and whipped cream and hold the filling for about two hours in the fridge. The shells can be baked a day ahead (store the cooled shells in an airtight container); fill them shortly before serving. The baked shells also freeze well; thaw before filling.

Adapted from Fine Cooking magazine, July 2006 issue. Tested by Susan Selasky for the Free Press Test Kitchen.

560 calories (61 percent from fat), 38 g fat (23 g saturated fat), 51 g carbohydrates, 8 g protein, 340 mg sodium, 205 mg cholesterol, 3 g fiber.