In a medium bowl, whisk together the flour, cocoa powder, baking soda, baking powder and salt. Then set aside.
1 ¾ cups (219 g) all-purpose flour, spooned and leveled, ½ cup (40 g) Dutch process cocoa powder, 2 ½ teaspoon baking powder, ¼ teaspoon baking soda, ½ teaspoon salt
In a large bowl, mix together the melted butter, sugar, eggs, milk, sour cream and vanilla.
½ cup (112 g) unsalted butter, melted, 1 cup (200 g) granulated white sugar, 2 eggs, at room temperature, ½ cup (120 ml) whole milk, at room temperature, ½ cup (122 g) sour cream, at room temperature, 2 teaspoon vanilla
Add the dry ingredients to the wet ingredients and mix until combined.
Add in the chocolate chips and fold them into the batter with a rubber spatula.
1 cup (200 g) mini semi-sweet chocolate chips
Cover the muffin batter with plastic wrap and let it rest at room temperature for 30 minutes.
Preheat the oven to 350 degrees and line a muffin pan with muffin liners.
After the batter has rested for 30 minutes, scoop the batter into the lined muffin cups. Sprinkle extra mini chocolate chips over each. (The best way to get extra domed muffin tops is to only add batter to every other muffin cup. If you don't have an oversized 24 capacity muffin pan, use two regular sized muffin pans.)
½ cup (100 g) mini semi-sweet chocolate chips
Bake the muffins for 20-23 minutes, or until a toothpick comes out from the centers with just a few moist crumbs.
After baking, let the muffins cool in the pan for 10 minutes. Then transfer them to a wire rack to finish cooling.