Preheat oven to 350°F (175°C) and position rack in center. Line a 12-cup muffin tin with paper cupcake liners.
Mash bananas in a medium bowl using a fork until mostly smooth with small lumps remaining. Don't blend completely smooth.
In a large bowl, whisk together flour, baking soda, baking powder, salt, and spices (if using) for 30 seconds to distribute leavening agents evenly.
In a separate bowl, whisk together mashed bananas, sugar, egg, melted butter, vanilla extract, and sour cream until well combined.
Pour wet ingredients into dry ingredients and fold gently with a spatula just until combined. A few flour streaks are fine—don't overmix.
Fold in any add-ins (chocolate chips, nuts, etc.) with 3-4 gentle strokes.
Fill each cupcake liner ⅔ full using a ¼-cup measuring cup or cookie scoop for uniform cupcakes.
Bake for 18-22 minutes until tops spring back when lightly touched and a toothpick inserted in center comes out clean or with just a few moist crumbs.
Rotate pan halfway through baking (at 10 minutes) for even browning if your oven has hot spots.
Cool in pan for 5 minutes, then transfer cupcakes to a wire rack.
Cool completely (20-30 minutes) before frosting.