Preheat the oven to 400ºF (200ºC). Line a 12-serving muffin pan with tulip liners*
In a large bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt.
In a separate large bowl, whisk together the granulated sugar, brown sugar, oil, eggs, vanilla extract, sour cream and milk until well combined. Stir the wet ingredients into the dry ingredients just until combined. Do not over mix. Fold in the chocolate chips.
Scoop the batter evenly into the muffin cups, about 3 1/2 oz (99g) in each one. Scoop or spoon a scant tablespoon-size dollop of the filling into the center of each muffin.
Bake for 5 minutes, then turn the oven temperature down to 350ºF (180ºC). Continue baking until a toothpick inserted into the cake part of the muffins comes out with a few moist crumbs on it, about 7-10 more minutes. If the toothpick hits a melted chocolate chip, reinsert a clean toothpick and test again. Cool in the pan for 5 minutes, then transfer to a cooling rack. Top each muffin with a quarter piece of Oreo cookie.