Passover Sponge Cake - cooking recipe

Ingredients

9 eggs, separated
2 c. sugar
6 Tbsp. water
2 1/2 tsp. grated lemon rind
1/4 c. lemon juice
1/2 tsp. salt
3/4 c. cake meal
3/4 c. potato starch

Preparation

Beat egg yolks with water, lemon juice and sugar until light and fluffy.
Gradually add cake meal, potato starch and lemon rind; mix well.
Beat egg whites with clean and dry blades until they are stiff (just until they leave peaks when blades are lifted).
Do not overbeat.
Fold into other ingredients very well; do not beat.