Preheat oven to 400 degrees F (200 degrees C). Line a jumbo or a 12 cups muffin pan with liners.
In a large bowl, sift or whisk All-Purpose Flour (2 cup), Baking Powder (2 teaspoon), Baking Soda (1 teaspoon), Salt (1/4 teaspoon) and Caster Sugar (1 cup). Set aside.
In another bowl, whisk Sour Cream (3/4 cup), Milk (3/4 cup), Large Egg (2), Clear Vanilla Extract (2 teaspoon) and Butter (1 cup).
Mix Semi-Sweet Chocolate Chips (1 1/2 cup) with about 2 tbsp of the dry ingredients.
Pour milk mixture to flour mixture and whisk until there’s no lumps. Fold in the chocolate chips. Divide batter into muffin pan, filling them up almost to the top.
For jumbo muffins, bake for 23-25 minutes or until a toothpick inserted in the middle comes out clean. For regular muffins, bake for for 16-18 minutes. For mini muffins bake for 9-12 minutes.
Allow muffins to cool in the pan for about 5 minutes, then transfer to a wire rack and allow to cool slightly before serving. Served warm or cool. Allow to cool completely before storing. Store leftovers in an airtight container to retain its moisture.