Heat oven to 350° F (175°C). In a food processor, process the cashews until finely ground. In a large bowl, whisk together the ground cashews, flour, cardamom, and grated clementine zest. Set aside.
Using an electric mixer, beat the butter and 1/3 cup (80 ml) of the powdered sugar on medium-high until light and fluffy, 2 to 3 minutes. Beat in the vanilla. Reduce mixer speed to low and gradually add the flour mixture, mixing until just combined (do not overmix).
Shape the dough into balls (about 1 tbsp/15 ml each) and place 2 in (5 cm) apart on baking sheets. Bake, rotating the baking sheets halfway through, until just beginning to brown, 12 to 14 minutes. Let cool slightly on the baking sheets, then transfer to a wire rack to cool completely.
Place the remaining 2/3 cup (160 ml) of powdered sugar in a clean ziptop bag. A few at a time, roll the cookies in the sugar to coat. Store in an airtight container in the fridge up to one week, or freeze up to a month.