Preheat the oven to 375°F and line a 12-cup muffin pan with paper liners. Zest and juice the oranges before preparing the batter so the citrus flavor stays fresh and vibrant throughout the recipe.
Whisk together the flour, baking powder, baking soda, and salt in a large bowl until evenly combined. This step ensures the muffins bake with a soft, even texture instead of dense pockets.
In another bowl, whisk the eggs and sugar until slightly creamy, then mix in melted butter, yogurt, vanilla extract, orange zest, and orange juice until smooth and fully blended.
Fold the wet ingredients gently into the dry ingredients until just combined. Avoid overmixing because too much stirring creates tough muffins rather than light and fluffy ones.
Divide the batter evenly into the prepared muffin pan and sprinkle coarse sugar on top if desired. Bake for 18 to 20 minutes until golden and cooked through.
Let the muffins cool in the pan for 5 minutes before transferring to a wire rack. Cooling briefly helps the muffins hold their shape and keeps the crumb tender.