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

2. In a large bowl, whisk together the all-purpose flour, 1/2 cup granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and the ingredients are evenly distributed.

3. In a separate medium bowl, whisk together the egg, whole milk, sourdough discard, melted and cooled butter, and vanilla extract until well combined and smooth.

4. Pour the wet ingredients into 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 more tender muffin.

5. Gently fold in the blueberries. If using fresh, they’ll mix in easily. If using frozen, add them directly from the freezer to prevent them from bleeding color.

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

7. Sprinkle the remaining 1 tablespoon of granulated sugar over the tops of the muffins. Bake for 20-25 minutes, or until the tops are golden brown and a wooden skewer inserted into the center of a muffin comes out clean.

8. Let the muffins cool in the muffin tin for 5 minutes before transferring them to a wire rack to cool completely. Enjoy them warm or at room temperature.