Preheat the oven to 350ºF. Lightly spray an 8 ½ x 4 ½-inch loaf pan with baking spray. In a medium bowl, whisk together the flour, salt, baking soda, baking powder, and cinnamon. In a separate medium bowl, stir together the mashed banana, sour cream (or yogurt), vanilla, vinegar and chopped nuts (if using). Set aside.