Preheat the oven to 375 degrees Fahrenheit. Line a 12-cup muffin pan with paper liners or lightly grease the muffin cups.

In a large mixing bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon until everything is evenly combined.

In a separate bowl, whisk the egg. Add the milk, vegetable oil, and vanilla extract. Continue whisking until smooth and fully combined.

Pour the wet ingredients into the bowl of dry ingredients. Stir gently using a spatula or wooden spoon until a thick batter forms. Do not overmix. The batter should remain slightly lumpy.

Add the chopped cranberries and gently fold them into the batter until evenly distributed throughout the mixture.

Divide the batter evenly among the prepared muffin cups, filling each cup approximately three-quarters full.

Sprinkle the tops with coarse sugar if using.

Bake for 18 to 22 minutes, or until the tops are lightly golden and a toothpick inserted into the center comes out clean.

Remove the pan from the oven and allow the muffins to cool in the pan for 5 minutes.

Transfer the muffins to a wire rack and cool completely before serving.