1. Preheat the oven to 350°F.
2. In a bowl, beat the eggs and sugar until the mixture is pale and thick.
3. Add the yogurt, flour, and baking powder. Mix well.
4. Add the lemon and orange zest. Mix.
5. Beat the egg whites until stiff peaks form. Add the beaten egg whites to the mixture and gently fold in with a spoon.
6. Pour the mixture into a greased and floured mold and bake for 55 minutes.
7. Remove from the oven and let cool in the mold on a rack before serving.