Preheat oven to 375F. Arrange bacon on a slotted broiler pan and bake to crisp 15-18 minutes.
If the bread you are using has a crispy crust, cut 12 slices and trim crust of 3. If using pre-packaged rather than freshly baked bread, this is unnecessary.
Slice and clean leeks, drain well. Heat 2 tablespoons butter in medium skillet. Add leeks and saut to tender, 3-4 minutes. Season with salt and pepper.
Build sandwiches: a slice of bread, Swiss slice, leeks, tomato slice, bacon, Swiss slice, trimmed (if using) crust slice of bread, cranberry sauce or chutney, cheddar, turkey, ham, cheddar, bread.
Heat griddle pan over medium heat. Rub griddle with butter.
Beat eggs with half-n-half. Coat sandwiches in egg batter. Griddle to deep golden under loose foil tent, 12-15 minutes turning occasionally.
For gravy, heat a skillet over medium heat with 2 to 3 tablespoons butter. Whisk in a couple rounded tablespoons of flour and add broth. Season with salt and pepper, Worcestershire and maple syrup. Cook to thicken up to coat spoon then stir in mustard.
Cut sandwiches corner to corner and serve with maple-mustard gravy dipper alongside.