Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it with cooking spray.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.
In another bowl, mix the melted butter, egg, buttermilk, orange zest, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix; a few lumps are okay.
Fold in the chopped cranberries until evenly distributed.
Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full.
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.