Preheat oven to 350°F. Line a muffin pan with liners or use a silicone muffin pan.
In a medium bowl, whisk together flour, baking powder, baking soda, salt, and cinnamon.
In a large bowl, mash bananas and stir in melted butter, maple syrup (or honey), sourdough discard, vanilla, and egg until smooth.
Add dry ingredients to wet ingredients and stir until just combined. Don’t overmix.
Fold in any add-ins like chocolate chips, nuts, or berries if using.
Divide the batter evenly between muffin cups, filling about ¾ full.
Bake for 20–23 minutes, or until muffins are golden brown and a toothpick comes out clean.
Cool on a rack before serving.