Preparation / Directions:
*to make 1 cup of Pesach confectioner's sugar, remove 1/2 tsp of sugar from 1 cup of granulated sugar and replace with potato starch
Cake: Preheat oven to 350 degrees. Grease a 10x15" jellyroll pan. Cover with wax paper; grease the paper. Beat the egg whites until soft peaks form. Gradually add 1/3 cup granulated sugar, beating until stiff peaks form. In a small bowl, beat the yolks until thick and lemon-colored. Gradually add 1/3 cup sugar, beating constantly. Stir in lemon juice and grated peel. Gently fold yolk mixture into the whites. Sift together the potato starch, matzah cake meal and salt. Gently fold, half at a tim, into the egg mixture until just blended. Spread batter evenly in the pan and bake 15 minutes or until the cake tests done. A wooden toothpick inserted in the center of the cake will come out clean. Remove from the oven and let cool for 5 minutes in the pan. Turn out onto a towel or aluminum foil that has been sprinkled generously with confectioners sugar. Roll up the cake and towel together from the long end. Let cool completely. Refrigerate rolled up while the filling is being prepared. Unroll the cake and spread evenly with the filling. Foll up and place on an ungreased cookie sheet, seam side down. Ice evenly the top and sides with meringue. Brown in the oven for 10 minutes at 350 degrees. Turn off the oven and allow cake to remain for 5 minutes. Place in the refrigerator until serving time.
Lemon Filling: Combine the sugar, potato starch and salt in a medium saucepan. Stir in the egg yolks, grated lemon peel, lemon juice and 3/4 cup water. Cook and stir over medium heat until bubbly. Boil 1 minute (only!). Remove from heat and stir in the margarine. Let cool without stirring. When filling is cool, assemble the cake roll.
Meringue: In a 1 quart saucepan, combine the potato starch and 1 tbsp sugar with 1/4 cup water. Bring to a boil; lower heat and simmer until thick. Cool. Beat egg whites until soft peaks form; add 1/4 cup sugar, 1 tsp at a time, potato starch mixture and vanill