Preheat oven to 350 degrees F and grease donut pan

In a mixing bowl combine flour, baking powder, baking soda, salt, and cinnamon

In another bowl whisk together brown sugar, egg, milk, sour cream, melted butter and vanilla extract

Slowly whisk the dry ingredients into the sugar and egg mixture until smooth and fully combined

Using a pastry bag, pipe the batter into the donut pan and fill each donut mold half way

Bake for 8-10 minutes or until the donuts spring back to touch

Allow the donuts to cool for 5 minutes and transfer to a wire rack

Combine the sugar and cinnamon topping in a bowl

Lightly brush the melted butter onto the baked donuts and immediately dip into cinnamon sugar topping and cover all sides