There is even a Wikipedia entry about it you can find here.
Here is the ingredient list for our take on the Jucy Lucy:
3 pounds of 80-20 ground chuck
Lawry's Seasoned Salt (to taste)
Cheese (whatever your favorite might be)
Any other spices and "fillings" you like in a burger. (My son likes onions, my husband likes mushrooms)
Take approximately 1/3 of a pound, gently flatten it, being careful not to work the meat too much. Place at least two slices of cheese in the middle, some ground pepper to taste, a little Lawry's to taste and your other favorite fillings. Gently flatten another 1/3 pound of ground chuck and place over the other patty with filling and pinch together. Repeat, until you've used up all the chuck.
Grill approximately 7 minutes per side, or until the meat reaches desired doneness.
Here is another blog about it
This is good stuff! Enjoy!!! I know I did!