Burger:

1. Preheat a griddle or large skillet over medium-high heat.
2. Shape beef into a small ball, about 2-3 inches in diameter.
3. Once the griddle or skillet is hot, place the patty on it.
4. Season with salt and pepper. Use the back of the spatula to quickly press down the patty into a thin shape. Cook for about 2-3 minutes, or until browned on one side.
5. Using a spatula, quickly flip the patty and sprinkle sliced onions on top. Cook for an additional 1-2 minutes.
6. Pour beef broth on the griddle or skillet and quickly cover it with cheese and the top bun to create steam. Let the sliders steam for about 30 seconds to 1 minute.

Assembly:

1. Toast bun.
2. Place the bun heel on plate.
3. Add the patty on top.
4. Finish with the top half of the bun.