Preheat the griddle to high heat.
Slice the sweet onion thin and set it aside.
Toast the brioche buns on the griddle.
Make 4 oz meatballs from the ground beef.
Use two spatulas to press the meatballs down as thin as possible on the griddle.
Season the burgers with salt and pepper.
Once the tops of the burgers start to become watery, flip them over.
Place a slice of cheddar cheese on top of each burger.
While the cheese is melting, make the sauce by mixing together the mayo, ketchup, mustard, and buffalo sauce in a small bowl.
Spread the sauce on both halves of the brioche buns.
Add a burger to each bun and top with a few slices of sweet onion.
Serve hot and enjoy!
