Begin by preheating your oven to 350°F (175°C). This ensures the muffins bake evenly.
Line a muffin tin with paper liners or grease it well with cooking spray to prevent sticking.
In a medium bowl, whisk together the unbleached all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
In a large mixing bowl, mash the ripe bananas until smooth. Add the melted unsalted butter, Greek yogurt (or sour cream), brown sugar, egg, and pure vanilla extract. Mix well until fully combined.
Gradually add the dry ingredient mixture to the wet ingredients. Gently fold the ingredients together with a rubber spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine.
Spoon the batter into the prepared muffin tin, filling each cup about three-quarters full. This allows room for the muffins to rise.
In a small bowl, mix the granulated sugar with a pinch of cinnamon. Sprinkle this mixture evenly over the tops of the muffin batter for a sweet, crunchy topping.
Place the muffin tin in the preheated oven and bake for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Once baked, remove the muffins from the oven and let them cool in the pan for about 5 minutes. Then, transfer them to a wire rack to cool completely. Enjoy warm or at room temperature!
