Prep your pan and oven. Heat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners or grease well.

Whisk the dry ingredients. In a large bowl, whisk 2 cups all-purpose flour, 3/4 cup sugar, 2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon fine sea salt.

Zest and juice the oranges. Zest one large orange to get about 1 to 1 1/2 tablespoons. Then squeeze 1/3 cup fresh orange juice. Set both aside.

Mix the wet ingredients. In a separate bowl, whisk 2/3 cup buttermilk, 1/2 cup neutral oil, 2 large eggs, the orange zest, the 1/3 cup orange juice, and 1 teaspoon vanilla until smooth.

Combine wet and dry. Pour the wet mixture into the dry bowl. Stir gently with a spatula until mostly combined. The batter should be thick and a little lumpy.

Fold in cranberries. Add 1 1/2 cups cranberries. If using fresh, roughly chop about half so you get a mix of juicy bursts and smaller berry pieces. Fold in gently. Do not overmix.

Portion the batter. Divide the batter evenly among the muffin cups, filling each about 3/4 full. Sprinkle the tops with coarse sugar if using.

Bake hot, then finish lower. Bake at 400°F (200°C) for 5 minutes to help create a tall dome. Without opening the oven, reduce heat to 350°F (175°C) and bake 13–16 minutes more, until a toothpick comes out with a few moist crumbs.

Cool and release. Let muffins cool in the pan for 5 minutes, then move them to a wire rack. This keeps the bottoms from getting soggy.

Enjoy. Serve warm or at room temperature. The orange flavor deepens by the next day.