Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan, or line it with parchment paper leaving an overhang.
Step 2: In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (2-3 minutes with an electric mixer).
Step 3: Beat in the eggs one at a time, ensuring each is fully incorporated. Stir in the vanilla extract, mashed bananas, and sour cream (or Greek yogurt) until just combined.
Step 4: In a separate medium bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
Step 5: Gradually add the dry ingredient mixture to the wet ingredient mixture, mixing on low speed (or by hand) until just combined. Be careful not to overmix; a few streaks of flour are okay.
Step 6: Pour the batter into your prepared loaf pan and smooth the top with a spatula.
Step 7: Bake for 55-65 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean or with moist crumbs attached.
Step 8: Remove from the oven and let cool in the pan on a wire rack for 10-15 minutes.
Step 9: Carefully remove the banana bread from the pan and let it cool completely on the wire rack before slicing and serving. This ensures the bread sets properly and slices cleanly.