Preheat oven to 350 degrees.
Line muffin tray with 12 regular size baking cups.
In a medium bowl, stir flour, sugar, baking powder and salt together with a wire whisk until combined.
In another bowl, stir sour cream, milk, eggs, vanilla and melted butter. Stir until combined.
Stir in chocolate chunks and divide batter into baking cups.
Bake for about 18-20 minutes or until done.
Makes 12 regular or 9 larger muffins. Bake a couple minutes longer for taller muffins.