1. Prepare your oven and muffin tin: Start by preheating your oven to 400 F (200 C). Line a 12-cup muffin tin with paper liners or grease it thoroughly with cooking spray. This prevents sticking and makes cleanup easier.

2. Combine dry ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt. Make sure there are no lumps and everything is well combined. This ensures even distribution of leavening agents.

3. Mix wet ingredients: In a separate medium bowl, whisk together the sourdough discard, milk, vegetable oil (or melted butter), egg, and vanilla extract until smooth. The mixture should be uniform in color and consistency.

4. Combine wet and dry mixtures: 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 help keep the muffins tender. Overmixing can lead to tough muffins.

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

6. Fill muffin cups: Divide the batter evenly among the 12 prepared muffin cups, filling each about two-thirds full.

7. Bake the muffins: Place the muffin tin in the preheated oven and bake for 18-22 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean. The tops should be set and lightly spring back when gently touched.

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.