In a large bowl whisk together the first 8 dry ingredients.
In another bowl whisk together the buttermilk, butter, eggs and vanilla. Then add into dry ingredients, stirring until just combined.
Scoop batter into prepared muffin tins and place in fridge for 30 minutes.
Bake at 375°F for 20-25 minutes.
While still muffins are still warm, brush tops with melted butter, then sprinkle with the cinnamon-sugar mixture (or roll tops in mixture to coat).