Combine dates, prunes, and hot water in bowl of a food processor. Process until a thick paste forms, about 20 seconds. Add cashews and cashew butter to date mixture. Process until well combined and mixture looks smooth, about 1 minute. Add goji berries, vanilla, and salt, and pulse until just combined, leaving some of the goji berries in larger pieces, 4 or 5 times.
Turn mixture out onto a parchment-lined work surface; roll into a 16-by-5-inch rectangle, about 1/2-inch thick. Cut into 8 (5-by-2-inch) bars. Refrigerate bars until firm and set, about 1 hour. Store bars in an airtight container between pieces of parchment at room temperature up to 2 days, or in the refrigerator up to 1 week.