Preheat the oven to 375°. Line 2 large baking sheets and 2 wire racks with parchment paper. In a large bowl, using a handheld electric mixer, beat the butter with 1/2 cup of the confectioners' sugar at medium speed until creamy. Add the vanilla extract. At low speed, beat in the flour, roasted cashews and salt. Scrape the dough onto 4 sheets of plastic wrap and form into 1-inch logs. Wrap the logs and refrigerate until firm, at least 20 minutes.