Preheat your oven to 350°F (175°C) and grease a standard muffin tin with butter or line it with paper liners.

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

In another bowl, combine the melted butter, lightly beaten egg, and buttermilk, mixing in the orange zest if using.

Pour the wet ingredients into the flour mixture and gently fold the ingredients until just combined, leaving some lumps.

Fold in the chopped cranberries until evenly distributed throughout the batter.

Spoon the batter into each muffin cup, filling each about ¾ full and sprinkle sugar on top for sweetness.

Bake in the preheated oven for 20-25 minutes or until golden brown and a toothpick inserted comes out clean.

Let the muffins cool in the tin for a few minutes before transferring to a wire rack to cool completely.