Heat your oven to 325°F/160°C. Grease and line a 9x5 inch loaf pan. Take 2 tablespoon of chips to the side for later.
In a stand mixer with the whisk attachment, cream your butter for 2-3 minutes, until smooth. Add both sugars and beat again until fluffy, about 3 minutes. Add the egg and beat again, then pour in the sour cream, milk and vanilla.
Sift the flour, cocoa powder, baking powder, salt, and baking soda straight into the mixing bowl, then add in the chocolate chips. Stir and fold with a rubber spatula until mixed and there are no more flour pockets.
Pour the batter into your loaf pan, it will be pretty thick! Use a small offset spatula to make figure-8's in the batter, this gets rid of any air pockets. Sprinkle 2 tablespoon of chips on top. Bake for 60-70 minutes. A toothpick inserted into the cake will come out clean.
Cool it in the pan for 15 minutes, then remove it and let cool completely.