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

2. 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 well combined; this ensures even distribution of leavening agents.

3. 3. Mix Wet Ingredients: In a separate medium bowl, whisk together the active sourdough starter, large egg, milk, melted and cooled butter, and vanilla extract until smooth. The starter should be bubbly and active for the best rise.

4. 4. Combine Wet and Dry: Pour the wet ingredient mixture into the dry ingredient mixture. Stir gently with a spatula or wooden spoon until just combined. Be careful not to overmix; a few lumps are perfectly fine and will lead to tender muffins. Overmixing can result in tough muffins.

5. 5. Fold in Chocolate Chips: Gently fold in the chocolate chips until they are evenly distributed throughout the batter.

6. 6. Fill Muffin Cups: Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full. You can use an ice cream scoop for easy and consistent portioning.

7. 7. Bake to Golden Perfection: Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a wooden skewer or toothpick inserted into the center of a muffin comes out clean. The tops should be golden brown and spring back when lightly touched.

8. 8. Cool and Enjoy: 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 prevent them from getting soggy on the bottom.