Preheat the oven to 375°F (190°C) and prepare a muffin tin.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix the buttermilk, egg, and vegetable oil until fully blended.
Add the zest and wet ingredients to the dry ingredients and stir until just combined.
Gently fold in the cranberries.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 18-20 minutes or until a toothpick comes out clean.
Remove from the oven and let cool for a few minutes before transferring to a wire rack.