In a blender (preferably a high-speed blender like a Vitamix), blend cashews and salt until they turn into a dense butter. Mix in peanut or almond butter, maple syrup, coconut oil, and vanilla and process until thoroughly combined.
Press mixture into a wax paper-lined loaf pan. Chill in the fridge at least 3 hours or in the freezer at least one hour. Cut into squares and serve. Keep in the freezer in an air-tight container for several weeks, or in the fridge for at least 2 weeks.