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 gluten-free oat flour, granulated sugar, baking powder, baking soda, ground cinnamon, and salt. Make sure there are no lumps and everything is evenly distributed.

3. In a medium bowl, mash the ripe bananas until smooth, with a few small lumps remaining if you prefer. Add the sourdough discard, melted butter, egg, and vanilla extract to the mashed bananas. Whisk until well combined.

4. Pour the wet banana 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 streaks of flour are perfectly fine. Overmixing can lead to tough muffins.

5. Divide the batter evenly among the 12 prepared muffin cups. You can use an ice cream scoop for easy portioning. Fill each cup about two-thirds full.

6. Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until the tops are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean.

7. Once baked, 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 them set and prevents them from getting soggy.