Step 1Heat the oven to 350 degrees.
Step 2Place the lemon juice and grated zest in a small saucepan. Bring to a slow boil. Simmer 4 to 5 minutes. (There should be 6 tablespoons of liquid. If not, add water.) Set aside to cool.
Step 3Using a fine-mesh strainer, sift together the matzo cake meal and potato starch 4 times. Set aside.
Step 4Place the egg yolks and whole egg in the small bowl of an electric mixer. Beat on medium speed until the mixture begins to thicken, about 3 to 4 minutes. Add 1 cup of sugar, 1 tablespoon at a time, and continue beating until the mixture turns pale yellow and is very thick. Scrape the sides of the bowl occasionally. Slowly add the oil in a steady stream.
Step 5Reduce the speed to medium-low. Add the cooled lemon juice and zest and beat until blended. Reduce the speed to low. Gradually add the sifted dry ingredients and mix until the batter is smooth. Transfer to a large mixing bowl. Set aside.
Step 6Place the egg whites in the large bowl of a mixer. Using clean beaters or the whip attachment, beat the whites on medium speed until frothy. Add the salt. Increase the speed to medium-high and gradually add the remaining 2/3 cup of sugar at the side of the bowl, beating until soft peaks form.
Step 7With a rubber spatula, fold 1/4 of the beaten whites into the yolk mixture to lighten it. Fold in the remaining whites.
Step 8Gently pour the batter into an ungreased 10-inch angel food pan with a removable bottom. Smooth the top. Bake in the lower 1/3 of the oven until the cake is golden brown and springy to the touch, 45 to 50 minutes.
Step 9Remove the cake from the oven and immediately invert the pan onto a wire rack. Cool the cake completely in the pan. Turn the cake upright and run a thin, sharp knife around the sides of the pan, then around the center tube. Lift the cake by the center tube and remove the ring. Run a knife under the cake to loosen the cake from the pan. Invert the cake and remove the tube section.
Step 10Transfer the cake to a platter. Store the cake at room temperature under a glass dome or cover with foil up to 1 week.