White Castle Hamburgers are the best and here is the recipe so you can make it at home.
Things You'll Need
You will want to make up the patties before hand and freeze them to have them turn out just right. 85% lean ground beef will work the best.
Take your ground beef, and divide into equal sized pieces. Make 8 patties or 12 patties. Form each into a 2−1/2 inch square patties. If you do this on waxed paper, it is easier to manage. You want to make the patties very thin. You will need to punch about 5-6 holes into the pattie. Go ahead and freeze.
When you are ready to cook, mince a medium white onion. Preheat your pan and spray it with non stick spray. Add about 1-2 tbs of onions into the pan for each pattie you are going to cook.
Put your frozen patties on top of onions and press down. You will cook the patties for about 3-4 minutes right on top of the onions. The holes that you put in the beef earlier will allow the patty to cook so that you will not have to turn it over. When it is done, add your salt and/or pepper.
Because the buns are small you will need to find dinner rolls that will fit the patties, but another way is to use hot dog buns. One hot dog bun makes two White Castle buns. All you have to do is cut the bun in half.