Producer Lisa Wagner shares her family recipe for sponge cake that includes a special surprise for Martha.
Heat oven to 325 degrees with rack in center. Whisk together matzo cake meal, potato starch, and salt; set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat yolks and 3/4 cup granulated sugar until thick and pale yellow. Gradually add dry ingredients, alternating with juice and zests.
In the clean bowl of an electric mixer fitter with the whisk attachment, beat egg whites until foamy. With machine running, gradually add remaining 1/4 cup granulated sugar and the salt. Continue beating until soft peaks form. Remove from mixer. Gently but thoroughly, fold egg whites into yolk mixture in two additions.
Pour into a nonstick 10-inch tube pan. Bake until golden, about 1 hour. Remove from oven, and invert onto a narrow necked bottle. Let stand until cool, about 1 hour, before removing pan. Will keep covered at room temperature for up to 3 days. Just before serving, dust with powdered sugar.