Beat butter and sugar in large bowl with electric mixer until creamy. Beat in egg unti light and fluffy. Mix in flour, lemon juice and zest, baking powder and salt. Cover, refrigerate about 2 hours or until firm.
Preheat oven to 180 C / Gas 4.
Roll out dough, a small amount at a time, to 6mm thickness on well-floured surface with floured rolling pin. (Keep remaining dough in refrigerator.) Cut with 7.5cm round pastry cutter. Transfer to ungreased baking trays. Sprinkle with sugar.
Bake 8 to 10 minutes until lightly browned on edges. Cool 1 minute on baking trays. Remove to wire racks; cool completely. Store in airtight container.