Chocolate Chunk Muffins    1 1/2 cup all purpose flour  1/2 cup sugar  1 1/2 teaspoons baking powder  1/2 teaspoon salt  3/4 cup sour cream  1/4 cup milk  2 eggs  2 teaspoons vanilla  1/4 cup melted butter, cooled slightly  6 oz. semisweet chocolate chunks        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, m...