Preheat oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease each cup generously with cooking spray; position the rack in the center of the oven.
Rinse cranberries under cold water, pat dry, and roughly chop into halves or thirds to help them distribute evenly and prevent sinking.
Zest one large orange to get 1 tablespoon of zest (orange layer only, no white pith), then halve and squeeze out 2 tablespoons of fresh juice, straining out seeds.
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt for about 30 seconds until evenly combined, then make a well in the center.
In a separate bowl, whisk together the melted (slightly cooled) butter, eggs, buttermilk, orange juice, orange zest, and vanilla until smooth and slightly frothy.
Pour the wet ingredients into the well in the dry ingredients and fold gently with a rubber spatula just until the flour is moistened — the batter should still look slightly lumpy; do not overmix.
Add the chopped cranberries and fold in with 3–4 broad strokes until evenly distributed; some berries may break and release juice, which is fine.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full, then sprinkle approximately 1/2 teaspoon of turbinado sugar over each.
Bake on the center rack for 20–22 minutes, until tops are golden brown, spring back when lightly touched, and a toothpick inserted in the center comes out with just a few moist crumbs.
Cool muffins in the pan for 5 minutes, then transfer to a wire rack and cool at least 10 more minutes before serving; enjoy warm or at room temperature.