Preheat oven to 350F (175C). Lightly grease a 6-quart cast iron pot.
In a medium bowl, whisk together flour, baking soda, and salt.
In a separate large bowl, cream together the softened butter and sugar until light and fluffy.
Beat in the eggs one at a time, then stir in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Fold in the mashed bananas and nuts (if using).
Pour batter into the prepared pot.
Cover the pot with its lid.
Bake for 45 minutes, then remove the lid and bake for an additional 10-15 minutes, or until a toothpick inserted into the center comes out clean.
Let cool in the pot for 10 minutes before transferring to a wire rack to cool completely.
Slice and serve.
Optional Tips: For a richer flavor, brown the butter before creaming it with the sugar. Add a teaspoon of cinnamon to the dry ingredients for a warmer spice profile. If the top of the bread browns too quickly, tent it with foil during the last 15 minutes of baking. Substitute gluten-free all-purpose flour blend for a gluten-free option.