Preheat oven to 425F and line a muffin tin with papers.
Sift the flour, cocoa powder, baking soda, baking powder, salt, and sugar into a large bowl. Whisk together and set aside.
In a separate bowl combine the eggs, vanilla, vegetable oil, sour cream, and milk then whisk together.
Set aside about 1/3 cup of the chocolate chips for the muffin tops.
Pour the wet into the dry and fold together using a spatula, mixing until almost combined. Sprinkle in the remaining chocolate chips and mix until the batter is just combined and the chocolate chips have been distributed.
Fill the muffin papers to the top and sprinkle with the reserved chocolate chips. Bake at 425F for 6 minutes then reduce to 350F and continue baking for about 14 minutes or until the centers are set, a toothpick or skewer inserted in the center will come out clean.
Don't use an electric mixer or you have a high chance of overmixing the batter. Just use a spatula and mix until everything is just combined.
Muffins don't take long to bake so try not to bake them for longer than instructed. To test that they are ready insert a toothpick into the center of one muffin and if it comes out clean with no wet batter they are ready.
Let them cool on a cooling rack before serving or storing.
Don't open the oven door or you risk the muffins deflating!
You can easily change up the flavors by adding in orange zest or even peppermint extract for a mint choc version.
Feel free to switch the chocolate chips for your favorites you could use white chocolate or butterscotch chips too.
The muffins will keep well for up to 3-5 days in an airtight container or can be frozen for up to 3 months.