Slice the roots and tips off the onions. Cut in half and slice into half rings.

Heat a medium skillet over medium heat and melt the butter.

Once the butter has melted add the onions and cook over medium low heat for 30 to 40 minutes, stirring every couple of minutes, until the onions are caramelized. Add a little water if the onions start to dry out or burn.

In a large bowl, stir together the beef base, onion powder, celery seed, parsley, and black pepper. Add the ground beef to the mixture and use your hands to work the seasoning all throughout the beef.

Break the mixture in half. Break each half into half again. Separate each portion into 3 chunks of meat and lightly roll into balls.

Heat a griddle or large skillet over high heat. Add enough butter to coat the bottom of the griddle or skillet.

Place the balls of meat at least 3 inches apart on the griddle and let cook on high for 2 minutes or until the bottoms are nicely seared.

Flip the meat over and immediately use a spatula to press the ball straight down to flatten it out. Continue cooking for 2-3 minutes and then flip. Top with cheese and continue cooking until the cheese has melted and the burger is done to your liking.

Repeat with remaining burgers as necessary until all are cooked, adding more butter to the griddle as necessary.

Place the burgers on the buns, top with the caramelized onions, and enjoy!