Preheat the oven to 175°C/fan 160°C.
Cream the butter, sugar, salt and vanilla using a stand-mixer fitted with the paddle attachement - although a hand-mixer works almost just as well - for 2-3 minutes, until light and fluffy.
Add the egg and yolk, and mix util combined.
Add the flour, baking powder and soda, and mix again on low speed until the dough just starts to come together.
In a separate bowl, mix the sugar and cinnamon for the coating and set aside until needed.
Place the dough on top of your work surface, and roll into a log. Divide in 4. Roll each piece of dough into a longer log, then divide in 6.
Roll each piece of dough into a ball, then coat in cinnamon sugar.
Place onto a baking tray lined with baking paper - around 8-9 cookies per tray, and bake for 12-14 minutes until the tops begin to crackle. As soon as the cookies come out from the oven, re-shape them using an upside-down glass or a round cookie cutter.
Allow to cool down and store in an air-tight container for up to 3 days.