PASSOVER SPONGE CAKE

Steps:

• Preheat the oven to 350 degrees. Grease a 9-by-9-inch baking pan with margarine. Dust pan with matzo meal; set aside.
• In the bowl of an electric mixer fitted with the whisk attachment, beat egg yolks on medium-high speed with 1/4 cup sugar until thickened, about 4 minutes. Transfer to a large mixing bowl. Wash and dry the mixer bowl and the whisk attachment.
• Place egg whites and salt in mixer bowl. Beat on medium speed with whisk attachment until soft peaks form. With machine running, slowly pour in the remaining 1/4 cup sugar; continue beating until stiff and glossy, about 3 minutes. Fold egg whites and orange zest into yolk mixture. Sift potato starch over the mixture, and fold in.
• Transfer the batter to the prepared pan. Bake until a cake tester inserted into the middle of the cake comes out clean, 10 to 15 minutes. Transfer pan to a wire rack, and let cool 15 minutes.