1. Mix yolks, 1/2 cup sugar, margarine, lemon rind, flour and baking powder.
2. In a separate bowl, beat egg whites, adding a half cup of sugar and beating until it forms stiff peaks.
3. Fold yolk mixture into whites.
4. Pour into the prepared baking pan. Bake at 350 degrees Fahrenheit for 25 minutes.
5. Line a 10- x 16-inch baking pan and set aside.