Begin by preheating your oven to 375°F (190°C). Prepare a muffin tin by lining it with paper liners or lightly greasing each cup with butter or cooking spray.
In a spacious mixing bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking powder, baking soda, fine salt, and ground cinnamon until well combined and free of lumps.
In a separate bowl, whisk together the melted butter, large eggs, freshly squeezed orange juice, pure vanilla extract, and orange zest until the mixture is smooth and well blended.
Gradually pour the wet ingredients into the dry ingredients, stirring gently with a spatula or wooden spoon just until the mixture comes together. Be careful not to overmix; the batter should have a few lumps for optimal texture.
Fold in the chopped cranberries and walnuts (if using), ensuring they are evenly distributed throughout the batter without overworking it.
Using a scoop or a spoon, divide the batter evenly among the 12 muffin cups, filling each approximately two-thirds full to allow room for rising.
Bake in the preheated oven for 18 to 22 minutes. To check for doneness, insert a toothpick into the center of a muffin; it should come out clean or with a few moist crumbs attached.
Once baked, allow the muffins to cool in the tin for about 5 minutes before gently transferring them to a wire rack to cool completely.
Notes
Serve warm, optionally dusted with powdered sugar or drizzled with orange glaze.