Preheat your oven to 425F (220C) and line a 12-count muffin tin with paper liners (or make my parchment paper liners and use them). Set aside.

In a large mixing bowl, whisk together flour, sugar, cornstarch, baking powder, baking soda, and salt.

In a separate medium sized mixing bowl, whisk together sour cream, melted butter, and egg until well-combined.

Add orange juice and zest to the sour cream mixture and whisk well.

Pour the wet ingredients into the dry ingredients and use a spatula to gently fold the wet and dry ingredients together until about just about 50% combined, then add cranberries and continue to gently fold until cranberries are well distributed and you have a uniform batter (batter will be thick, do not over-mix or your muffins will be dense).

Evenly divide batter into your prepared muffin tin and sprinkle tops with additional granulated sugar.

Bake in the center rack of 425F (220C) oven for 8 minutes, then without opening the oven door, reduce the oven temperature to 350F and bake for another 8-10 minutes, until a toothpick inserted in the center of the muffin comes out clean or with a few moist crumbs.

Allow muffins to cool in their pan for 5-10 minutes before carefully removing from pan and allowing to cool completely on cooling rack.