Cream the butter, shortening and sugar. Add the eggs and vanilla and beat for one minute.
Add the flour, salt and baking powder and mix well. Add the cranberries, ginger and white chocolate chips.
Place half the dough on 24″ of plastic wrap and roll into a log about 2″ thick. Do the same with the other half. Refrigerate for 3 hours or overnight.
Preheat the oven to 375 degrees. Unwrap the dough and slice into pieces about 1/4″ thick and place 2″ apart on a baking sheet.
Bake for 10 minutes, until edges have just started to brown. Let cool for 5 minutes on the baking sheet then transfer to a rack to finish cooling.