Banana Sour Cream Cake

• 4 egg whites
• 1 egg
• 1/4 prunes pureed
• 850 ml nonfat vanilla yogurt
• 325 gr flour
• 250 gr sugar
• 190 gr mashed bananas about
• 55 gr margarine (light)
• 3 gr baking powder
• 3 gr baking soda