Sift flour, baking powder and bicarbonate of soda into a bowl. Stir in sugar. Make a well. Add egg, vanilla and milk. Stir well to combine.

Combine extra sugar and cinnamon in a shallow bowl.

Add enough oil to a large, deep frying pan to come 4cm up side of pan. Heat over medium-high heat (see note). Drop 1 tablespoon of batter into oil. Repeat 5 more times. Cook, turning, until doughnuts are puffed and golden all over. Using a slotted spoon, transfer doughnuts to a plate lined with paper towel to drain. Toss doughnuts in cinnamon mixture to coat all over. Transfer to a baking paper-lined wire rack. Repeat with remaining batter and cinnamon mixture.