In a large mixing bowl sift together the cake flour and cocoa powder. Add the granulated sugar, baking powder, baking soda, salt, espresso powder, and chocolate chips, and whisk to together until combined.
2 cups (250g) Cake flour, ½ cup (43g) Unsweetened Dutch process cocoa powder, 1 cup (200g) Granulated sugar, 2 ½ teaspoons Baking powder, ½ teaspoon Baking soda, ½ teaspoon Kosher salt, 1 teaspoon Espresso powder, 1 ½ cups Mini semisweet chocolate chips
In a medium mixing bowl, whisk together the eggs and sour cream until smooth. Then mix in the vanilla extract, melted butter, oil, buttermilk, and melted chocolate.
2 large Eggs, ¼ cup (60g) Sour cream, 1 tablespoon Pure vanilla extract, ¼ cup (57g) Unsalted butter, ¼ cup (56g) Vegetable oil, 1 cup (240g) Buttermilk, 4 oz Semisweet chocolate bar (56%)
Pour the wet ingredients into the dry ingredients. Using a rubber spatula, gently fold the batter until just combined.
Cover the bowl with plastic wrap and let it rest for 1 hour at room temperature.
After 1 hour, preheat the oven to 425F. Line a 12 cup cupcake tin with 6 paper liners, placing each liner in every other muffin cup. For this method, you will be baking the muffins in two batches. Be sure to cover the batter while the first batch bakes. Alternatively, you can bake all at one time but your muffins will not rise as tall.
Using a large ice cream scoop, gently scoop the fluffy muffin batter into the paper liners, taking care not deflate the batter. Overfill each liner to the top. Top with chocolate chips and an extra sprinkle of sugar.
Bake for 5 minutes at 425F. Then (without opening the oven door), lower the oven temperature to 375F and bake for an additional 15 minutes.
Let the muffins rest in the pan on a wire rack for 5 minutes, then transfer each muffin to a cooling rack to cool completely. Allow muffins to cool for an additional 10 minutes. Enjoy!!
Note: If baking the muffins in two batches, be sure to increase the oven temperature back to 425F once the first batch of muffins are done baking. While the first batch of muffins are baking, cover the remaining batter with plastic wrap until you are ready to bake the second batch.