Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan, or line with parchment paper for easy removal.
Step 2: In a medium bowl, whisk together the flour, baking soda, ground cinnamon, and salt. Set aside.
Step 3: In a large bowl, using an electric mixer, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2-3 minutes.
Step 4: Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Step 5: Gently fold in the mashed bananas until just combined. Be careful not to overmix.
Step 6: Gradually add the dry ingredients to the wet ingredients, mixing on low speed or by hand with a spatula until just combined and no streaks of flour remain. Do not overmix; a few lumps are fine.
Step 7: If using, gently fold in any optional mix-ins like chocolate chips or nuts.
Step 8: Pour the batter into the prepared loaf pan and spread evenly.
Step 9: Bake for 60-70 minutes, or until a wooden skewer or toothpick inserted into the center of the loaf comes out clean or with a few moist crumbs attached (no wet batter). If the top browns too quickly, loosely tent with foil.
Step 10: Remove from the oven and let cool in the pan on a wire rack for 10-15 minutes. Then, lift the loaf out of the pan using the parchment paper (if used) and transfer directly to the wire rack to cool completely before slicing and serving.