Preheat the oven to 400˚F. Grease 18 muffin cups or line with paper liners.
In a small bowl, mix together the milk and vinegar. Set aside to “sour”.
In a medium bowl, beat together 1 cup white sugar and butter until light and fluffy. Beat in the yogurt. Add in the eggs one at a time, beating in between each addition.
In separate bowl, mix together the flour, salt and baking soda. Slowly mix into the sugar mixture until fully incorporated. Pour in the “soured” milk, and stir until just combined. Fold in the orange zest.
Scoop the batter into the prepared muffin cups, filling each about 3/4 full. Bake for 12-14 minutes, or until a toothpick inserted in the center comes out clean.
When the muffins are almost done baking, mix together the sugar and orange juice in a small saucepan over medium heat. Heat until the sugar is dissolved.
When the muffins are done, remove from the oven and brush the orange syrup over the tops of the muffins. Allow to cool for a few minutes before removing from the pan.