Get a pound of 85% lean ground beef, and divide into 16 equal sized pieces.
Form each into a 2−1/2 inch square patties. Do this on waxed paper. Make
the patties very thin. Then "cookie−cut" five holes in each pattie.
(the pattern should resemble 5 on a dice) A CLEAN pen cap works nicely.
Freeze these 16 patties. (It'll make it easier later)

BUNS: the buns are also small. My grocer has dinner rolls the exact size
I need, but you might have to create your own using hot dog buns. One
hot−dog bun makes two White Castle buns. Simply cut in half (through top
and bottom) and then cut off the rounded sides to make them square.

COOKING: This is key. You need to finely chop a medium white onion.
On a pre−heated 375 degree electric griddle, lay about 1−1/2 Tablespoons
of onion for each patty you want to cook (generously spray with non−stick
spray like Pam first) The onions should only be "one deep" if you will.
Immediately place frozen patty directly on top of onions and press down.
Cook for about 4 minutes right on top of the onions. The holes in the beef
will allow the steam to cook the top side. (You don't flip)
Add a dash of salt and a pinch of pepper to each patty while they cook.
Remove and place on UNTOASTED buns.