I first heard about this sandwich in preparation for National Grilled Cheese Day. The sandwich incorporates the World's Best Mac & Cheese into their famous grilled cheese sandwich. The product of which is an ooey-gooey mess of cheesey goodness.
Not listed on the menu, it is certainly one of Pike Place's tastiest secrets. But it's up to the person working as to whether or not you can get your hands on it. So ask real nice and maybe throw a little something in the tip jar and they just might allow you a taste of grilled cheese heaven.