re: Burger sliders for a party

get a sheet pan and spread the ground meat out thinly in the pan...you can put a sheet of plastic wrap over the meat and roll thin with a beer bottle or something

take a pizza cutter and cut into the size squares you want

you can do several sheet pans like this

spread grated onion over the top

put under the broiler till crusty, pull and flip them, then crust the other side.
it will only take a minute or two each side