Cream the butter and sugar well. Beat in the egg yolk and vanilla. Sift together the flour, baking powder and salt, then fold into the creamed mixture until a soft dough begins to form. Finally add the white chocolate, cranberries and pistachios.

Form the cookie dough into a log 2 inches in diameter. Wrap in plastic wrap and store in the refrigerator. The dough should be chilled for at least a couple of hours but can be kept in the fridge for several days so you can bake as many or as few as you like and bake the rest later when needed.

Preheat the oven to 350 degrees F and with a sharp serrated knife, cut off 1/2 inch thick slices of cookie dough and place on a parchment lined cookie sheet. Bake for about 20 minutes or until they turn golden at the edges. Cool on the pan for 5 minutes before transferring to a wire rack to finish cooling. Store in an airtight container.