1. 1. Prepare Your Oven and Muffin Tin: Start by preheating your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or grease it well with butter or cooking spray. This prevents sticking and makes cleanup easier.

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

3. 3. Combine Wet Ingredients: In a separate medium bowl, whisk together the sourdough starter discard, milk, melted butter (or oil), lightly beaten egg, and vanilla extract until well combined. The mixture should be smooth.

4. 4. Add Mashed Bananas: Gently fold the mashed ripe bananas into the wet ingredient mixture. The bananas should be very ripe, with plenty of brown spots, as this contributes to the muffins’ sweetness and moisture.

5. 5. Combine Wet and Dry Mixtures: 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 lumps are perfectly fine and will result in a tender muffin. If using, fold in the chocolate chips or chopped nuts at this stage.

6. 6. Fill Muffin Cups and Bake: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full. Place the muffin tin in the preheated oven.

7. 7. Check for Doneness: Bake for 20-25 minutes, or until the muffins are golden brown and a wooden skewer or toothpick inserted into the center of a muffin comes out clean.

8. 8. Cool and Serve: 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. Enjoy them warm or at room temperature.