1. In a bowl combine flour, baking powder and baking soda.
2. In a separate bowl mix butter and sugar until well combined.
3. Add eggs and mashed bananas to butter mixture.
4. Add to flour mixture to the butter mixture. Add yogurt and mix together well (until smooth).
5. Spoon batter into lightly greased baking pan and top with walnuts (if using).
6. Bake at 350 degrees for about 35 minutes or until baked through.