Preheat oven to 425°F (218°C). Line or grease a 12-count muffin pan.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In another bowl, whisk sugar, eggs, milk with vinegar (or buttermilk), sour cream, oil, butter, and vanilla until smooth.
Gently fold the wet mixture into the dry until just combined. Batter will be thick. Fold in the chocolate chips.
Let the batter rest for 20 minutes in the refrigerator.
Spoon batter into muffin cups, filling nearly full. Sprinkle tops with extra chips and coarse sugar if desired.
Bake at 425°F (220°C) for 5 minutes. Without opening the oven, reduce the temperature to 350°F (175°C) and bake for 15–18 minutes more, or until a toothpick inserted in the center comes out clean.
Cool muffins in the pan until mostly cooled, then transfer to a wire rack to cool completely.
Notes
Start baking at high heat for domed tops.
Mini chocolate chips disperse better, but you can use regular chocolate chips too!
Store muffins at room temp up to 3-4 days or freeze for 3 months.