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)

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

In a heavy noncorrodible saucepan, beat the egg yolks and sugar with a wooden spoon until well blended. Stir in the lemon juice, butter, and salt. 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.) 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.)

When the curd has thickened, pour it at once into the strainer. Press it with the back of a spoon until only the coarse residue remains. Discard the residue. Stir in the lemon zest.

Tips:

• 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.

From Rose's Christmas Cookies, by Rose Levy Beranbaum, William Morrow and Company Inc., New York, 1991 Photo by Louis Wallach