Preheat oven to 425°F. Line the muffin pan with muffin/cupcake liners, or grease with oil spray or butter. Set aside.
In a large bowl, whisk together the flour, baking powder, salt, and cinnamon.
In a separate large bowl, whisk together the eggs, sour cream, and sugar until well blended. Pour in the milk, vegetable oil, melted butter, and vanilla extract; whisk together to combine. Gently fold the wet ingredients into dry ingredients until well blended. Avoid over-mixing at this stage. Then gently fold In chocolate chips just until incorporated into the batter.
Using a ¼ cup measuring cup or a large ice cream scoop, scoop the batter into the prepared muffin pan. Fill each muffin liner all the way to the top. Sprinkle lightly with additional cinnamon and coarse sugar.
Bake at 400°F for 5 minutes. Then, reduce the oven temperature to 350°F and continue to bake for 22-25 minutes, just until the tops are lightly golden brown and a toothpick comes out clean when you gently test it in the middle of a muffin.
Remove muffins from the pan and cool on a cooling rack for 5 minutes before serving.
Notes
Makes: 12 to 15 muffinsTo make the cinnamon sugar: I always keep a small mason jar full of cinnamon sugar mix to top muffins, French toast, waffles, and more. Simply use a ratio of 2 to ½ - two parts granulated sugar to one-half part ground cinnamon. These muffins will stay fresh for 5-7 days at room temperature when stored in an airtight container.Freezer instructions: Store in a freezer safe container and freeze for up to 3 months. When ready to serve, thaw muffins in the refrigerator or on the counter.Double the recipe: You can double the recipe to make a double batch. Make one now, freeze one batch for later!