1. Preheat your oven to 400 F (200 C). Line a 12-cup muffin tin with paper liners or grease it well with butter or non-stick spray.

2. In a large mixing bowl, whisk together the cornmeal, all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed.

3. In a separate medium bowl, whisk together the sourdough discard, buttermilk, melted butter, and the large egg until well combined. The mixture should be smooth.

4. Pour the wet ingredients into the dry ingredients. Stir gently with a spoon or spatula until just combined. Do not overmix; a few lumps are perfectly fine. Overmixing can lead to tough muffins.

5. Divide the batter evenly among the 12 prepared muffin cups. Each cup should be about two-thirds full.

6. Place the muffin tin in the preheated oven and bake for 18-22 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. Remove the muffins from the oven and let them cool in the muffin tin for 5 minutes before transferring them to a wire rack to cool completely. Serve warm or at room temperature.