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 non-stick spray. This step ensures your muffins won’t stick and makes for easy cleanup.

2. Combine dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed. This creates the base for your muffins.

3. Mix wet ingredients: In a separate medium bowl, whisk together the sourdough discard, milk, melted butter, egg, and vanilla extract until well combined and smooth. The discard should be fully incorporated into the liquid mixture.

4. Combine wet and dry mixtures: Pour the wet ingredient mixture into the dry ingredient mixture. Using a spatula or wooden spoon, gently fold them together until just combined. Be careful not to overmix; a few lumps are perfectly fine and will lead to a more tender muffin. Overmixing can result in tough muffins.

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

6. Bake until golden: 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. Cool and serve: Once baked, remove the muffin tin from the oven and let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely. This prevents them from getting soggy on the bottom.