Preheat your oven to 400°F (200°C). Grease a 12-cup muffin tin or line it with paper liners to prevent sticking.
In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
In a separate medium bowl, beat the egg lightly. Whisk in the milk, vegetable oil, orange juice, and orange zest until the mixture is smooth.
Pour the wet ingredients into the dry ingredients. Use a spatula to stir them together just until moistened. Be careful not to overmix, as this can make the muffins tough.
Gently fold the cranberries into the batter. If using frozen berries, do not thaw them first to prevent the color from bleeding too much into the batter.
Spoon the batter evenly into the prepared muffin cups. Bake for 18 to 22 minutes, or until a toothpick inserted into the center comes out clean. Let them cool in the pan for 5 minutes before moving them to a wire rack.