Preheat your oven to 375°F. Line or grease a 12-cup muffin pan with paper liners.
In a large bowl, whisk together the flour, baking powder, cinnamon, and salt.
In another bowl, whisk together the milk, sugar, oil, eggs, and vanilla extract.
Stir the wet ingredients into the dry ingredients. Be careful not to overmix...the batter should be slightly lumpy.
Fold in the chocolate chips.
Divide the batter evenly among the muffin liners.
Bake for 20-25 minutes until a toothpick inserted into the center comes out clean (a few crumbs are okay, but there should be no streaks of wet batter).
Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.