1. Preheat your oven to 375 F (190 C). Line a 12-cup muffin tin with paper liners or lightly grease each cup.

2. In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, and salt until they are well combined.

3. In a medium bowl, whisk the egg until lightly beaten. Then, add the milk, vegetable oil, and vanilla extract, mixing until everything is fully incorporated.

4. Pour the wet ingredients into the dry ingredients. Stir with a spatula or wooden spoon just until combined. Do not overmix; a few lumps are fine.

5. Add the chopped fresh cranberries and the orange zest to the batter. Gently fold them in until they are evenly distributed. Avoid overmixing.

6. Divide the batter evenly among the 12 prepared muffin cups, filling each cup about two-thirds full.

7. Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until the tops are golden brown and a wooden skewer inserted into the center of a muffin comes out clean.

8. Once baked, remove the muffins from the oven and let them cool in the muffin tin for 5 minutes before transferring them to a wire rack to cool completely.