Add brisket to slow cooker. Pour in bourbon and maple syrup. Cook on low for 8 hours until tender.
Remove and shred meat with forks. Save some juices if needed for moisture.
Butter bread slices. In a skillet, layer cheddar and brisket between two slices, buttered sides out.
Cook sandwiches 2–3 minutes per side until golden and melty.
Warm waffles until crisp.
Place each grilled cheese between two waffles. Serve hot.