Preheat oven to 375 degrees and line muffin tins with liners or spray with non-stick spray. Set aside.

In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda and salt.. Set aside.

In a large bowl with the stand mixer or hand mixer, beat the eggs on medium speed. Slowly add the sugar while continuing to beat until the mixture turns a thick, white pale color. Beat in the oil until combined. Wipe down the bowl and add the sour cream and vanilla until well-combined. Being careful not to over mix.

Add the dry ingredients to the wet ingredients and gently fold it in using a rubber spatula until everything is just barely mixed. Add the chocolate chunks and almost all of the dark chocolate chips (leaving some to sprinkle on the tops of the muffins) and mix until just combined.

Spoon the batter evenly into the muffin tins, filling them up until they're almost full. Sprinkle with a few chocolate chips and sparkling sugar.

Bake muffins in preheated oven for 10 minutes, then reduce the heat to 350 degrees and bake another 5-10 minutes (I did about 7) until a toothpick inserted in the center comes out clean. Cool muffins in pan for about 10 minutes and transfer to cooling rack to cool completely.

Store muffins in closed air-tight container at room temperature for up to one week or in the freezer for two months.