Passover Sponge Cake

DIRECTIONS

1. Preheat oven to 325 degrees F (165 degrees C). Cut parchment paper to line the bottom of a 10 inch tube pan. Do not grease the pan.
2. In a medium bowl, whip egg yolks until light. Gradually add 1 cup sugar and orange zest; continue whipping until thick and pale, about 7 minutes. Sift together the matzo cake meal and potato starch; set aside. In a large glass or metal mixing bowl, beat egg whites until foamy. Gradually add remaining 1/2 cup sugar, continuing to beat until whites form stiff peaks. Fold the dry ingredients into the yolk mixture alternately with the juice. Fold 1/3 of the whites into the batter, then quickly fold in remaining whites until no streaks remain. Spread evenly into the prepared pan.
3. Bake for 1 hour and 10 minutes in the preheated oven, until cake springs back to the touch. Invert onto a wire rack to cool. Run a knife around the sides of the cake before removing from the pan.