1. Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it thoroughly.

2. In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking soda, salt, and ground cinnamon (if using). Make sure there are no lumps and the ingredients are evenly distributed.

3. In another medium bowl, mash the ripe bananas until mostly smooth with a few small lumps remaining. Add the sourdough discard, milk, melted butter (or oil), egg, and vanilla extract. Whisk these wet ingredients together until well combined.

4. Pour the wet ingredient mixture into the bowl with the dry ingredients. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will lead to tender muffins. Overmixing can result in tough muffins.

5. If you’re using chocolate chips or chopped nuts, gently fold them into the batter until evenly distributed.

6. Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full.

7. Bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back lightly when touched.

8. Remove the muffin tin from the oven and let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely. This helps prevent them from getting soggy on the bottom.