### Instructions:
1. Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line it with parchment paper.
2. In a large bowl, cream butter and brown sugar together until fluffy. Beat in the eggs one at a time, then stir in the mashed bananas and vanilla extract until smooth.
3. In a separate bowl, whisk together flour, baking soda, salt, and cinnamon if using.
4. Fold the dry ingredients into the banana mixture just until combined—don’t overmix. If using sour cream and nuts, fold them in here.
5. Pour batter into prepared pan and bake for about 55–60 minutes, or until a toothpick inserted in the center comes out clean. If the top browns too fast, tent loosely with foil for the last 10 minutes.
6. Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.
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### Notes & Tips:
* Use very ripe bananas—the browner and sweeter, the better—for maximum flavor and moistness.
* Adding sour cream or yogurt ensures a tender, rich crumb that stays soft for days.
* Customize your loaf with walnuts, chocolate chips, or a cinnamon-sugar crust for extra texture and flavor.
* For a subtle twist, a teaspoon of espresso powder can deepen the flavor and balance sweetness.
