Preheat the oven to 400℉. Line a muffin tin with paper liners (or spray with nonstick spray).
In a small bowl, whisk together the milk, melted butter, sour cream, egg and vanilla extract.
In a large bowl, combine the flour, sugar, baking powder and salt. Add the liquid ingredients to the dry ingredients; stir until the batter is combined. Stir in ¾ cup of the chocolate chips.
Spoon the batter into the prepared muffin cups, filling each ⅔ full. Sprinkle the remaining chocolate chips on top.
Bake 15 to 18 minutes, until the muffins test done.