Passover Sponge Cake

2 eggs
7 egg yolks
1 1/4 cups granulated sugar
1 teaspoon grated lemon rind
3 tablespoon lemon juice
1 cup potato starch
7 egg whites
Fresh strawberries and blueberries

Combine eggs and egg yolks; beat at high speed of electric mixer until well blended. Gradually add sugar, 1 tablespoon at a time, beating at medium speed. Add lemon rind and lemon juice, and beat well. Fold in potato starch.

Beat egg whites (at room temperature) at high speed until stiff peaks form; fold into batter. Pour batter into an ungreased 10-inch tube pan with removable bottom. Bake at 350 degrees F for 45 minutes. Invert pan; let cool 1 hour. Loosen cake from sides of pan, using a narrow metal spatula; remove from pan.

Serve with fresh berries.