Ultimate Lemon Butter Bar
Yield: 18 Servings
For shortbread base:
Pat the dough into the prepared pan. Use a fork to prick
the dough all over.
For lemon curd topping:
In a heavy non-reactive saucepan, beat the yolks and sugar until well blended. Stir in the lemon juice, butter and salt. Cook over medium-low heat, stirring constantly (be sure to scrape the sides of the pan), until thickened and resembling hollandaise sauce, which thickly coats a wooden spoon but is still liquid enough to pour. 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 come to a boil or it will curdle. Whenever steam appears, remove the pan briefly from the heat, stirring constantly, to keep the mixture from boiling. When the curd has thickened, pour it at once into the strainer. Press with the back of a spoon until only the coarse residue remains. Discard the residue (or enjoy it as a treat--it tastes great). Stir gently to mix in the zest sitting in the bowl.
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, and return it to the oven for 10 minutes. Cool the lemon curd-topped shortbread completely in the pan on a wire rack. Refrigerate the pan for 1 hour to set the lemon curd completely before cutting into bars.
Run a small metal spatula between the sides of the pan and the pastry on the 2 sides without the aluminum foil. Use the foil to lift out the lemon curd-covered shortbread onto a cutting surface. Using a long sharp knife, cut the shortbread first in thirds, then in half the other way, and then cut each half in thirds. Wipe the blade after each cut.
Place powdered sugar in a strainer and tap the strainer with a spoon to sprinkle a thick, even coating over the lemon curd. (The powdered sugar will start to be absorbed into the lemon curd after several hours, but it can be reapplied before serving. The lemon bars may be stored in an airtight container for 3 days at room temperature, 3 weeks in the refrigerator, or 3 months in the freezer.
Smart Cookie Tips:
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.
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.