Simple Bakery-Style Banana Chocolate Chunk Muffins

0 Start by lining a muffin pan with muffin liners (or grease each cup if you’re skipping liners). Set the pan aside and preheat your oven to 400°F. This high temperature helps create tall, fluffy muffins.
1 In a large mixing bowl, stir together the all-purpose flour, granulated sugar, baking soda, baking powder, and salt. Mix thoroughly so your dry ingredients are evenly distributed.
2 In a separate bowl, whisk together the mashed bananas, sour cream, milk, vegetable oil, eggs, and vanilla extract. Make sure everything is well combined and smooth—room temperature ingredients blend much more easily.
3 Make a well in the center of the dry ingredients, then pour in the wet mixture. Gently fold everything together by hand until no large streaks of flour remain. Be careful not to overmix, or you’ll end up with rubbery muffins. The muffin batter should be thick and slightly lumpy.
4 Fold in the chocolate chunks, distributing them evenly throughout the batter.
5 Using a large ice cream scoop or measuring cup, fill each muffin cup about ¾ full. If you like, sprinkle a few extra chocolate chunks and a pinch of sugar on top for a crisp finish.
6 Bake for 5 minutes at 400°F. Then, without opening the oven, reduce the temperature to 350°F and continue baking for 20–25 minutes. 
7 The muffin tops should be golden brown, and a toothpick inserted in the center should come out clean.Cool the muffins in the pan for 5 minutes, then transfer to a wire rack to cool completely before storing.