Preheat the oven to 430°F and line a muffin pan with 12 liners.
In a medium bowl, whisk together the dry ingredients: flour, kosher salt, baking powder, and cinnamon. Set aside.
Using a fork or mixer, mash the overripe bananas in a large mixing bowl.
Add the vegetable oil, sour cream, eggs, vanilla extract, and dark brown sugar to the mashed bananas. Beat until well combined.
Gradually add the dry ingredients to the wet ingredients in two batches, beat until just combined.
Gently fold in the raspberries, being careful not to overmix.
Distribute the batter evenly among the 12 muffin liners. The liners will be full. If desired, sprinkle the tops with a little granulated or turbinado sugar for added texture and sweetness.
Place the muffins on the center rack of the oven to ensure even baking, avoiding placement too close to the top or bottom and immediately reduce the temperature to 400°F
Bake for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and let them cool in the pan for 5 minutes before transferring to a wire rack to cool completely.