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1. Place butter and sugar in a bowl and beat until pale and creamy.
2. Beat in egg then stir in orange zest and juice.
3. Sift flour, baking soda and cream of tartar over the creamed mixture and then stir to combine. 
4. Cover bowl and refrigerate mixture for 2 hours.
5. Heat oven to 180 deg;C. Line two baking trays with non-stick baking paper. Place sugar in a bowl.
6. Roll tablespoonfuls of the mixture into balls, then roll in sugar to coat. 
7. ress sugar-coated balls on to oven trays, leaving space for the cookies to expand during cooking.
8. Bake for 12 to 15 minutes or until golden brown. Remove to a wire rack to cool completely.

Tip: Stored in airtight containers, all these types of biscuit will  last well for up to five day.