Preheat the oven to 375°F. Line a 12-cup muffin pan with cupcake liners or spray with non-stick cooking spray.
Sift together the flour, cocoa powder, salt, baking powder, baking soda, and sugar in a small bowl and set aside.
In a large mixing bowl, beat or whisk together eggs, melted butter, vanilla extract, buttermilk, and sour cream.
Dump the dry ingredients into the butter/eggs/sour cream mixture and stir gently, just until combined. Do not overmix.
Add the chocolate chips and stir just until they are distributed throughout the batter.
Divide batter between the 12 muffin cups in the prepared pan, filling each cup about ¾ of the way full.
Bake for approximately 20 minutes or until a toothpick inserted in the center of the muffins comes out clean.
Cool muffins in pan for 5 minutes. Remove muffins to a cooling rack to finish cooling.
Notes
Do not over stir the batter. The muffins will be too dense and tough.
Tossing chocolate chips in a little bit of flour before adding them to the batter will help to keep them suspended in the batter for even distribution.
An ice cream scoop is a great way to fill muffin cups mess-free.
Do not leave the muffins to cool in the baking pan. The heat from the pan will overcook them.