Preheat oven to 160 C / Gas mark 3. Cut baking parchment to line the bottom of a 25cm tube cake tin. Do not grease.
In a medium bowl, whip egg yolks until light. Gradually add 225g of caster sugar and the orange zest; continue whipping until thick and pale, about 7 minutes. Sift together the matzo meal and potato starch; set aside.
In a large glass or metal mixing bowl, beat egg whites until foamy. Gradually add remaining sugar, continuing to beat until whites form stiff peaks.
Fold the matzo meal 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 cake tin.
Bake for 1 hour and 10 minutes in the preheated oven, until cake springs back to the touch. Run a knife around the sides of the cake and turn out onto a wire rack to cool.