Passover Citrus Sponge Roll

SPONGE ROLL: Preheat Oven to 350 degrees. Beat egg whites until stiff, adding half the sugar gradually; set asside. Using the same beater, beat the yolks while adding the remaining sugar, until mixture is very light. Stir lemon juice, rind, potato starch and salt into yolks. Gently fold in whites, starting with a quarter of the mixture, then adding the rest. Gently spread onto a cookie sheet lined with parchment paper and lightly sprayed with non-stick vegetable oil spray. Gently smooth the surface. Bake for 10 - 15 Minutes or until sponge has risen slightly and is lightly browned. Remove from oven and turn cake out onto a clean cloth. Allow to cool. Spread Orange filling evenly over cake and gently roll up using cloth to help lift cake. Sprinkle with sugar &/or whipped cream - etc. ORANGE FILLING: Combine sugar, potato starch, orange juice and lemon juice in a saucepan and bring to a boil. Boil 1 minute, while stirring constantly. Remove from heat. In a separate bowl, beat egg yolks. Stir a little bit of orange mixture into egg yolksm then add yolks to the sauce pan. Cook gently for one minute. Stir in 2 tablespoons margarine, allow mixture to cool before using.