Preheat your oven to 350°F (175°C) and liberally grease a 12-cup muffin tin with butter.

In a medium mixing bowl, whisk together the flour, baking soda, salt, and cinnamon. Set aside.

In a separate large mixing bowl, using an electric mixer at medium speed, cream together the brown sugar and butter until fluffy and significantly lighter in color.

Beat the eggs into the creamed butter, one egg at a time, scraping down the batter as needed. Then, mix in the vanilla extract and sour cream. Set aside.

In a small bowl, mash the bananas with a fork until they are pretty smooth but still have some small chunks.

Beat the mashed bananas into the creamed butter and sugar mixture. Then, with the mixer on low, gradually add the flour mixture to the creamed mixture and mix until just combined; don't overmix. Finally, using a rubber spatula, fold in the walnuts. The batter will be thick.

Spoon the batter into the prepared muffin tin, filling each cup almost to the brim. Brush the tops of the muffins with melted butter and sprinkle a liberal pinch of raw cane sugar over each.

Bake for 22-26 minutes or until a toothpick inserted into the center of a muffin comes out clean.

Remove from the oven and let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely.