In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, sugar, and orange zest until light and fluffy, about 5 minutes.
Beat in the vanilla, then mix in the salt and flour until just combined.
Stir in the cranberries and pistachios.
Divide the dough in half and roll each portion into a log. Use plastic wrap to shape the logs into rectangles so the cookies will slice into squares later. Chill in the refrigerator at least 2 hours, or overnight.
Preheat the oven to 325°F. Line two baking sheets with parchment paper.
Slice the chilled dough into squares about ½ inch thick and arrange on the prepared sheets.
Bake 12–15 minutes, until set but not browned. Let cool completely on a wire rack.
Transfer the melted white chocolate to a piping bag (or a zip-top bag with a corner snipped off) and drizzle over half of each cookie. Alternatively, dip half of each cookie directly into the chocolate. Sprinkle with extra orange zest if desired.
Allow to cool until the chocolate hardens, then serve or store in an airtight container for up to a week.
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