In a small bowl, combine mayo, ketchup, and sweet pickle relish. Set aside.

Divide two pounds of ground chuck into 12 equal pieces. Form into mini burgers.

Liberally salt and pepper both sides of each burger.

Melt one tablespoon butter over medium heat in a large frying pan. Toast the buns. Set aside.

Melt an additional tablespoon butter in the pan and turn the heat up to high. When the pan is hot, add burgers. You may need to cook them in two batches if your pan isn't large enough. Allow the burgers to cook for three minutes per side. When the burgers are almost done, add a slice of American cheese.

When the burgers are cooked to your preferred doneness, remove them from the pan and place on a bun. Top with special sauce, and raw onion if desired. Serve immediately.