Call them whatever you wish, I don't care. Growing up in the south I ate pert nert a ton of Krystals long before I heard of White Castle. I can devour either or both, at the same time!
Here's how I putem together at home.....
First I order dried chopped onions, big sack, from Pendery's in Texas. While awaiting their arrival I make sure to gather up sufficient cheap yellow mustard, cheap thin sliced dill pickles, cheap fat ground beef, American cheese slices "right size" buns and potato chips, paper plates and napkins. I get out the well seasoned castiron griddle which sits atop two stove eyes. If thats too small, I have another which covers the entire stove top.
Dried onions arrive. Pour them into a big pot, cover with 4 or 5 times volume of water overnightish.
Now were ready to get cooking. Steam the onions. This may be done ahead, just refrigerate. Big broad pot of water allowing for an "onion pan or rack" to hold an abundance of chopped onions. Set this up, top the onions with salt pepper and whatever you wish. Flip and turn the onions until about half cooked. Get that cheap meat rolled out thinly between layers of plastic wrap on a cutting board. Using a pizza cutter, cut out the appropriate size patties, then using the handle end of a wooden spoon make 5 spaced indentations through each patty. Bring the griddle up to temp. Have a semi trained friend ready to assist, iced down beverages(one in hand), along with good friends and a beautiful New Mexico sunset...........
TURN ON the kitchen vent fan... Cover the grill with a generous amount of the onion, very closely slap down the meat patties, top with the bottom half of the bun then the top half. Cook..... When done, top with the "stuff" and enjoy.
MY way for 15 or 20 folks. No complaints, they keep coming back.