Whisk together the flour, cocoa powder, baking powder, baking soda and salt in a medium mixing bowl.
2 cups all purpose flour, 1 cup unsweetened cocoa powder, 2 1/2 teaspoons baking powder, 1/2 teaspoon baking soda, 1/2 teaspoon salt
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.
2 large eggs, 1 1/4 cups granulated sugar, 1/2 cup vegetable oil, 1 1/2 cups sour cream, 1 tablespoon vanilla extract
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. Mix until just combined. Cover the bowl with a towel and let the batter rest for 15 minutes.
5 ounces semi sweet chocolate, 5 ounces dark chocolate chips
While it's resting, preheat the oven to 425°F and line muffin tins with liners or spray with non-stick spray. Set aside.
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.
sparkling sugar
Bake muffins in preheated oven for 7 minutes, then reduce the heat to 350°F and continue baking for another 10-12 minutes, or until a toothpick inserted in the center comes out clean. Cool muffins in pan for 10 minutes then transfer to cooling rack to cool completely.
For leftover muffins, line a airtight container with paper towels to absorb extra moisture. Close the lid and store at room temperature for up to 4 days or in the fridge for up to 1 week.