Preheat your oven to 375°F (190°C). Grease or line a muffin tin with paper liners.
In a large mixing bowl, whisk together the flour, sugar, baking powder, baking soda, salt, and optional cinnamon.
In another bowl, combine the melted butter, milk, eggs, and vanilla extract. Whisk until well blended.
Pour the wet ingredients into the dry ingredients and stir gently, being careful not to overmix. Fold in the cranberries.
Evenly distribute the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake for 18-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove from the oven and let the muffins cool in the tin for about 5 minutes before transferring to a cooling rack.
If desired, sprinkle a little sugar on top of the muffins before baking for added sweetness.
Store leftover muffins in an airtight container at room temperature for up to 3 days or freeze for up to 3 months.