In a large mixing bowl, add All-Purpose Flour (1 cup), Baking Powder (3/4 teaspoon), Baking Soda (3/4 teaspoon), Brown Sugar (1/3 cup) and Ground Cinnamon (1 teaspoon). Mix together.
In a small mixing jug, add Vanilla Yogurt (1/2 cup), Egg (1) and Vanilla Extract (1 teaspoon). Mix together until completely combined.
Add the wet ingredients into the dry ingredients and mix to combine.
Transfer the batter to a plastic bag. Cut a small hole in the bottom corner of the bag and squeeze the batter into a lightly greased donut pan, filling each hole about 3/4 of the way.
Bake at 180 degrees C (350 degrees F) for about 10 minutes, until donuts have risen and are lightly golden.
Allow donuts to cool for 5 minutes.
To make the cinnamon sugar, stir together Caster Sugar (1 cup) and Ground Cinnamon (1 teaspoon).
Dip each donut in Butter (100 gram) and coat in cinnamon sugar.