Combine flour, baking powder, salt, zest and cranberries; mix well and set aside. Cream butter, beat in icing sugar. Add egg and beat well. Mix in flour mixture.
Divide dough in half, forming each half into a roll approximately 10 inches long and 1 1/2 inches in diameter. Dough will be quite soft. Wrap and refrigerate for at least 3 hours or until firm. (Make ahead: Refrigerate for up to 3 days or freeze in airtight container for up to 3 weeks. Let stand at room temperature for 20 minutes.)
Preheat oven to 375°F. Cut each roll into slices 1/4 inch thick and place on prepared cookie sheet. Bake for 10 – 12 minutes or until a light golden colour.