In a medium-sized bowl, combine the flour, baking soda, salt, and cinnamon. Mix thoroughly and set aside.
Using a mixer with a paddle attachment, beat the softened butter and brown sugar at high speed for about 2 minutes until creamy.
Reduce the mixer speed to medium and incorporate the eggs one by one, ensuring to blend well after each addition. Mix in the yogurt (or sour cream), mashed bananas, and vanilla extract until smooth.
On low speed, gradually integrate the dry ingredients into the wet mixture, mixing until just combined without any visible flour. If using nuts, gently fold them into the batter now.
Pour the batter into the prepared loaf pan and level the surface. Bake for 60 to 65 minutes, tenting with foil halfway through to avoid excessive browning. Start testing for doneness at 60 minutes with a toothpick.
Once baked, allow the bread to cool in the pan on a wire rack for around an hour. Then, remove from the pan and let it cool completely before slicing.
To store, keep your banana bread covered at room temperature for up to 2 days, or refrigerate for up to a week. It tastes best after a day or two, when the flavors meld beautifully.