Prepare a 12-cup muffin tin by greasing the cups well. Preheat the oven to 400 degrees F. (205 degrees C.).
In a large mixing bowl, add the starter or discard, milk, oil, sour cream, and egg. Use a fork to whisk well to fully combine.
Add the sugar and vanilla, and stir well to combine.
Add the cocoa, flour, baking soda, and sea salt. Stir until just combined.
Add almost all of the chocolate chips to the batter, reserving a few to sprinkle on top of the muffins before baking if desired.
Fold the chocolate chips into the batter.
Divide the batter evenly among the muffin cups. If using, sprinkle the tops of the muffins with reserved chocolate chips.
Bake the muffins until the tops are firm and the middles cooked through, about 20 minutes.
Cool the muffins for 5 minutes in the muffin tin before removing them to cool on a wire rack. Eat warm or at room temperature.
Notes
I’ll often grease a second muffin tin and bake 24 smaller muffins for about 15 minutes instead of 12 large muffins. This makes them go farther in a bigger family and helps to reduce toddler waste when they can’t finish a bigger muffin. Plus, the smaller muffins fit nicely in lunch boxes.
You can use sour cream or plain Greek yogurt for this recipe. I prefer to use the full fat versions. Reduced fat sour cream or plain Greek yogurt leads to a muffin that is drier in texture.