Instructions

1. Preheat oven to 375ºF and grease a standard 12-cup muffin pan with cooking spray, wiping off any excess spray on the top of the pan.
2. In a bowl, whisk (or better yet sift) together the flour, cocoa powder, baking powder, baking soda, and salt.
3. In the bowl of a stand mixer fitted with the whisk attachment (or using a handheld electric mixer), begin beating the eggs on medium-high speed. Slowly stream in the sugar while beating and continue to beat until the mixture is pale and thickened and ribbons down from the beater when lifted before settling back down into the batter (see photo in post above). Wipe down the bowl and beater as needed.
4. Beat in the oil until fully incorporated. Wipe down bowl and beater and beat in sour cream and vanilla until evenly incorporated.
5. Add the dry ingredients to the wet and fold in just until only a few visible streaks remain. Add 8 1/2 ounces of the chocolate and fold in just until all ingredients are evenly incorporated. The batter will be thick!
6. Spoon the batter evenly into the prepared muffin cups, smoothing the tops if needed but keeping the scoops mounded; fill all 12 muffin cups completely. Sprinkle the remaining chocolate and sparkling sugar on top.
7. Bake muffins in preheated oven for 10 minutes, and then reduce heat to 350ºF and bake another 7-12 minutes, until a toothpick inserted into the center of one comes out clean, or with just a few moist crumbs or streaks of melted chocolate. Cool muffins in pan for about 15 minutes before transferring to a wire rack to cool completely. Store muffins in an airtight container at room temperature, or in the refrigerator to keep for more than a few days.