Preheat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease the cups.
In a medium bowl, whisk together the flour, baking soda, and salt. Set aside.
In a large bowl, whisk together the melted butter, oil, brown sugar, and granulated sugar until smooth. Add the eggs, sour cream, and vanilla extract, and whisk until well combined.
Stir in the mashed bananas until evenly incorporated.
Gently fold the dry ingredients into the wet ingredients using a spatula until just combined. Be careful not to over-mix the batter.
Divide the batter evenly among the muffin cups, filling them about 3/4 full. If desired, sprinkle with coarse sugar.
Bake at 400°F (200°C) for 5 minutes. Then, reduce the temperature to 350°F (175°C) and continue baking for 15-18 more minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Allow the muffins to cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.
Notes
Store in an airtight container at room temperature up to 2 days.
For tips, step-by-step photos, and extra details, be sure to read the full post above before starting. It’s packed with helpful info to answer common questions!