Preheat the oven to 320°F/160°C (350°F/175°C for light metal pans) and grease or line a 9-inch loaf pan.
In a bowl, sift together cake flour, baking soda, and salt. If adding walnuts (or other mix-ins), take a couple spoonfuls of the flour mixture into a separate bowl and toss the walnuts with it. Set aside.
In a large bowl, cream together softened butter and sugar. Add the eggs, banana, yogurt, milk, and vanilla and mix until combined.
Add the dry ingredients into the wet ingredients and stir only until combined. Fold in the walnuts and pour into the prepared loaf pan.
Bake for 1 hour 15 minutes and test for doneness with a skewer (spaghetti works well too!). Let it cool in the pan for 5 minutes before transferring to a wire rack to cool completely.