Preheat oven to 400℉/205℃. Line a muffin tin with 12 liners and set aside.
In a medium-sized bowl, sift the dry ingredients and mix together. Set aside.
2 cups all-purpose flour, 1 1/4 cup white sugar, 1/2 cup unsweetened cocoa powder, 1 tsp baking soda, 2 tsps baking powder, 1/2 tsp salt
In a large bowl, add the wet ingredients. Whisk until well combined (1-2 minutes).
2/3 cup vegetable oil, 2 large eggs, 1 egg yolk, 1/2 cup milk, 1 cup sour cream, 1 tbsp vanilla
Add the dry ingredients into the wet. Using a spatula, gently fold until a batter forms. Do not over-mix!
Toss in the chocolate chips and mix in a few times.
3/4 cups semi-sweet chocolate chips
Evenly divide the batter between 12 liners, they should be almost or all the way full. Sprinkle extra chocolate chips and white sugar on top (optional, but recommended).
Bake the muffins at 400°F for 15-18 minutes. The muffins are ready when a toothpick inserted comes out clean.
Allow to cool and enjoy! These muffins are delicious and so easy to bake.