Break up the room temperature butter with a pastry knife.
Thoroughly knead with the pastry knife until the mixture is homogeneous and doesn't stick to the mixing bowl.
Add the cranberries and the zest, and hand-mold into a cylinder.
Roll the cylinder in parchment or wax paper so that the cylinder is smooth. Freeze for one hour.
Make slices in the frozen dough with your sharpest serrated knife.
Bake at 325F for 11 minutes on an ungreased cookie sheet.
Great with tea!