In a medium saucepan, add the oil and set over medium heat.
Once hot, add the diced onion and sauté for 3 minutes. Add the water and Worcestershire sauce. Bring to a simmer and for 8 minutes. Remove from heat and set aside.
Between two sheets of parchment paper, flatten the beef into a rectangle until the beef is evenly ¼” thick. Add the salt and pepper to each side of the beef.
Preheat the oven to 350°f
Cut the beef into 12 patties.
Using a metal straw or wooden spoon handle, perforate vent holes into each patty. This allows the burgers to be steamed, the way White Castle does.
On a baking sheet, add the onions and juices, spreading them out across the entire sheet.
Place the patties on top of the onion.
Place the baking sheet into the oven, cover with a larger baking sheet that’s turned upside down.
Bake for 10 minutes.
While the burgers steam cook in the oven, cut the rolls in half to make a bun.
When the burgers are done remove the top baking sheet carefully and then carefully remove the burger sheet.
Assemble the sliders with a bottom bun, then a burger patty, divide the slices of cheese to fit the patties, then top with 2 pickles, ketchup, and or mayonnaise. Toppings are optional.
Add the top bun and enjoy!
Notes
Nutritional information is an estimate and will vary based on your specific ingredients.