Preheat oven to 350°F (180°C) and grease a 12-cup muffin tin.
Mix together the milk and vinegar in a small bowl and set aside for about 10 minutes.
Whisk together the flour, sugar, baking soda, cream of tartar, salt, and cinnamon in a large mixing bowl.
Pour in the milk mixture, oil, and vanilla and stir until just combined.
Evenly distribute the batter into the muffin tin, filling all 12 cavities.
Bake for 20-24 minutes, until a toothpick comes out clean or with only crumbs. Once baked, allow to cool while you prepare the coatings.
Place the melted butter in a small bowl. Stir together the sugar and cinnamon in a separate small bowl.
For each muffin, remove from the pan and gently coat in the melted butter, then place in the cinnamon sugar mixture and coat well. Set on a serving tray.