Preheat the oven to 425°F (220°C). Line a 12-cup muffin pan with paper liners or grease well.
Mix the wet ingredients. In a large bowl, mash the bananas. Stir in the granulated sugar and brown sugar. Whisk in the egg for 1–2 minutes until the mixture is lighter in color. Add the melted butter, vanilla, and Greek yogurt (or sour cream), and whisk until smooth.
Mix the dry ingredients. In a separate bowl, whisk together: Flour, Baking soda, Baking powder, Salt, Cinnamon (if using)
Combine. Gently fold the dry ingredients into the wet ingredients with a spatula just until no streaks of flour remain. Do not overmix.
Fill the muffin cups. Divide the batter evenly among the 12 muffin cups. They should be nearly full.
Bake using the bakery method. Bake at 425°F for 5 minutes. Without opening the oven door, reduce the temperature to 375°F (190°C) and continue baking for 15–18 minutes, or until a toothpick inserted into the center comes out clean.
Cool. Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.