Light Banana Bread

Name: Light Banana Bread
Ingredients: Nonstick baking spray with flour (see note); 1 1/2 cups (7 1/2 ounces/213 grams) unbleached all-purpose flour; 1/2 cup (2 ounces/57 grams) cake flour; 1 teaspoon baking powder; 1 teaspoon baking soda; 1/2 teaspoon salt; 3/4 cup (5 1/4 ounces/149 grams) sugar; 3 very ripe, darkly speckled large bananas (about 1 1/4 pounds), mashed well (about 1 1/2 cups); 1/4 cup plain low-fat yogurt; 1 teaspoon vanilla extract; 3 tablespoons unsalted butter , softened; 2 large eggs; 1/4 cup walnuts , chopped (optional)