I got around 26 cookies from the above qty. You can store the cookies in an airtight container for a week.
If you dont have cream of tartar with you you can use baking powder. Omit both cream of tartar and bicarbonate of soda from the recipe and use baking powder instead. You may use 1 1/4 tsp of baking powder.
Substitute for Castor sugar: to get 1 cup caster sugar, process 1 cup granulated sugar (usual sugar) in a food processor/mixer until fine, but don’t powder it like icing sugar.