Preheat your oven to 400°F (200°C).
Line a 12-cup muffin tin with paper liners or grease lightly.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt until well combined.
In a separate bowl or measuring jug, whisk the egg, milk, oil, vanilla, orange zest, and orange juice until smooth.
Make a well in the dry ingredients. Pour the wet ingredients into the center and gently fold with a spatula until just combined. A few streaks of flour are fine.
Add the cranberries and fold in only until distributed. Do not overmix or the muffins will be dense.
Divide the batter evenly among the muffin cups, filling them about 3/4 full.
Sprinkle the tops with coarse sugar if using.
Bake for 16–20 minutes, until the tops are golden and a toothpick comes out with a few moist crumbs.
Cool in the pan for 5 minutes, then transfer to a rack to cool completely or serve warm.