Combine sunflower oil, sugar, eggs, sour cream, vanilla, baking powder, baking soda and salt in a large bowl and whisk to blend well. Whisk in cocoa powder.
Sift flour over the bowl and fold it in gently and quickly followed by the milk before all of the flour is incorporated. Fold in 1 cup of mini chocolate chips. Be careful not to over mix.
Cover the bowl and set aside while the oven preheats. Preheat the oven to 425°F and line a standard muffin pan with 12 paper liners.
Use an ice cream scoop or large spoon to divide the batter evenly among lined muffin cups, filling them right to the top. Don’t mix it around or bother it too much. Top each muffin with the remaining mini dark chocolate chips. Don’t be shy with those chocolate chips because they will spread out as the muffins rise in the oven.
Bake at 425°F for 10 minutes. Then, with the oven door still closed, reduce the oven temperature to 350°F and bake for another 8-10 minutes until a skewer inserted into the center comes out clean despite any melted chocolate chips. Let muffins cool for 5 minutes in the pan and then transfer muffins to a cooling rack. They’re best served warm!