Preheat oven to 425°F (218°C). Line a muffin pan with paper liners or lightly grease it.
In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt.
In a medium bowl, whisk eggs, oil, milk, vanilla, and sourdough discard until smooth.
Pour the wet ingredients into the dry ingredients and mix gently until just combined. Do not overmix.
Fold in 1 ½ cups of chocolate chips, saving the rest for topping.
This recipe makes 12-14 muffins. Divide batter between muffin cups, filling almost to the top. Sprinkle remaining chocolate chips on each.
Bake at 425°F for 6 minutes, then reduce temperature to 350°F without opening the oven door. Bake for another 15–17 minutes or until a toothpick comes out clean.
Cool in the muffin pan for 10 minutes, then transfer to a cooling rack to cool completely.