Place butter and sugar in the bowl of an electric mixer. Beat until well combined. Add zest, juice and egg. Mix well.
In a clean bowl, sift together the plain flour, baking powder, cinnamon and salt, then gently fold in the almond flour until well combined.
Add the flours to the butter mixture and fold through until a soft dough forms. Cover and refrigerate for at least 2 hours.
In the meantime, preheat oven to 170°C fan forced and line oven trays with baking paper.
Place icing sugar into a bowl. Roll tablespoons of dough into balls and toss into the icing sugar so that they are well coated. Place onto oven trays 3 cm apart to allow for spreading and bake for 12 minutes.
Remove from the oven and allow to cool for 5 minutes before transferring to a wire rack to cool completely. Dust with a little more icing sugar (if desired).