Add milk chocolate chips, heavy whipping cream, and maple syrup to slow cooker. Cover and cook on high for 1 hour (keep the lid on the whole time!).
Add white chocolate chips to the slow cooker and stir until the white chocolate melts (you may need to cover and allow it to cook for 10 minutes or so, then stir again). Stir in vanilla and spices.
Pour melted chocolate into an 8" x 8" parchment paper lined pan. If desired, sprinkle coarse sea salt or more spices over chocolate. Allow to cool completely (1-3 hours). Cut into squares. Store in airtight container at room temperature.