Preheat the oven to 200 C / Gas 6. Grease a baking tray or line with baking parchment.
Cream together the margarine and 170g (6 oz) sugar until light and fluffy. Add the egg and the vanilla extract and mix well. Sift in the flour, bicarbonate of soda and cream of tartar and mix until well blended and smooth. Set aside.
In a separate bowl, combine the 2 tablespoons caster sugar and cinnamon. Take a teaspoon of biscuit mixture at a time and lightly coat with the sugar and cinnamon mixture, press down slightly to form round discs and arrange well spaced out on the prepared tray.
Bake in preheated oven for approximately 10 minutes until the biscuits are firm and golden brown.