Preheat your oven to 350°F.
In a large mixing bowl combine the dry ingredients: flour, sugar, baking soda, baking powder, cinnamon and salt. Whisk together.
In a separate mixing bowl combine the wet ingredients: sourdough starter, sour cream, vanilla, egg. Whisk all together.
Add in cooled melted butter to the wet ingredients and whisk.
Add the dry ingredients to the wet ingredients and mix together just until all of the flour is hydrated. Make sure not to over mix.
Grease your muffin pan if you're not using muffin liners.
Spoon approximately 2 tablespoons of muffin batter into each portion.
Bake for 18-20 mins. Don't over bake or it will be dry.
Once the muffins are slightly cools, dip the tops in melted butter, and then dip into another bowl with cinnamon sugar.
Enjoy!