Spray 3 1/2- to 4-quart slow cooker with cooking spray. In slow cooker, mix all ingredients except cashews and vanilla.
Cover; cook on Low heat setting 2 hours.
Line cookie sheets with waxed paper. Stir mixture in slow cooker until smooth. Add cashews and vanilla; stir until cashews are coated. Drop mixture by heaping tablespoonfuls onto cookie sheets. Let stand until firm. Store tightly covered at room temperature.