Preheat the oven to 425 F (218 C) for at least 30 minutes before baking. Line (2) 12 ct. muffin pans with cupcake liners.
In a mixing bowl, sift the flour, unsweetened cocoa powder, baking powder, baking soda and salt together, then whisk together until well combined. Then whisk in the light brown sugar and granulated sugar until well combined.
2 cups (240 g) all purpose flour, ½ cup (40 g) unsweetened cocoa powder, 2 teaspoons baking powder, ½ teaspoon baking soda, ½ teaspoon salt, ½ cup (100 g) granulated sugar, ½ cup (100 g) light brown sugar
In another bowl whisk the eggs until lightly beaten. Then whisk the eggs, oil, buttermilk, sour cream, vanilla extract and espresso powder until smooth and well combined.
2 large eggs, room temperature, ½ cup (120 ml) oil , ¾ cup (180 ml) buttermilk, room temperature , ½ cup (120 g) sour cream, room temperature, 2 teaspoons instant espresso powder, 2 teaspoons (10 ml) vanilla extract
Stir the dry ingredients into the wet ⅓ at a time. Before mixing in the last ⅓ of the dry ingredients, toss the mini chocolate chips into the dry ingredients. Then mix the remaining dry ingredients, along with 1 - 1¼ cups chocolate chips into the wet ingredients. Do not overmix.
1½ cup mini or regular chocolate chips or chocolate chunks, divided
For bakery style muffins, alternate filled and unfilled muffin wells. Use a 3 tablespoon sized cookie scoop to scoop the fudgy muffin batter into each of the muffin liners, alternating every other cup.Top the muffins with the reserved ¼ cup chocolate chips or granulated sugar if you like. Bake the muffins at 425 F (218 C) for 5 minutes. Then reduce the oven temperature to 350 F (177 C) to bake the chocolate muffins for another 12 - 14 minutes (for a total baking time of 17 - 21 minutes). The muffins are done when a toothpick inserted into the center comes about with a few moist crumbs or when a finger pressed gently into the center of the muffins quickly bounces back. Cool the double chocolate muffins in the muffin pan for 5 - 10 minutes. Carefully remove the muffins to cool to room temperature and enjoy.